Effect of frying media and packaging materials on shelf life of tengolalu-a deep fat fried snack

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1 Wudpecker Journal of Food Technology Vol. 1(3), pp , May Wudpecker Journals Effect of frying media and packaging materials on shelf life of tengolalu-a deep fat fried snack Anil babu 1, N.S Vijayalakshmi 1, B.S Roopa 2, V. Vishalakshi 1, A.G Gopalakrishna 3, K. Srinivasulu 1 and A.R Indiramma 1* 1 Food packaging technology, 2 Sensory science, 3 Lipid science and traditional foods Central Food Technological Research Institute, Mysore *Corresponding Author nsvijayalakshmi@yahoo.com Accepted 02 May 2013 Tengolalu an Indian deep fat fried snack was prepared by frying in four different refined vegetable oils, Coconut oil, Palm oil, Ground nut oil and Sunflower oil. This was packed in two packaging materials 75µ polypropylene and 12µ metallised polyester/50µ HDPE-LDPE which varied a lot in their oxygen transmission. The products were exposed to 30-40% RH and C. The products were subjected to physico-chemical and sensory analysis during periodic withdrawals of every 10 days. Sunflower oil, Ground nut oil, Palm oil and Coconut oil could offer <20 days, 30 days, 40 days and 60 days shelf life respectively. Increase in peroxide value and rancid odour terminated the shelf life. The shelf life was in commensuration with degree of unsaturation of oils. For this dry product, hydrolytic rancidity which is predominant in saturated oils like Coconut oil was not observed up to 60 days of storage period studied. Key words: Tengolalu, Refined vegetable oil, Coconut oil, Palm oil, Groundnut oil, Sunflower oil, Shelf life, material. INTRODUCTION Deep fat fried products that add variety to the diet form the largest group of snack foods marketed in India. A large number of fried snacks varying in composition, method of preparation, shape, size, texture and flavour are being prepared and consumed. These include moist snack foods like samosa, cutlets, vada etc. having high moisture content of 15 to 40% with very short shelf life and crispy snack foods like banana and potato chips with a lower moisture content of 2 to 4% with a longer shelf life. A large number of fried items are made from flours of wheat, bengal gram, black gram and rice. The oil used as frying medium has a great impact on the, texture and keeping-quality of the final product. Because of very low moisture content, the products are highly susceptible to autoxidation of fat which results in off- flavors and rancidity in the product. Some oils are more prone to rancidity than others, which can be an important factor in selecting the oil as frying medium. Generally, oil which is widely available at the lowest cost is being used for frying (Arya, 1992). Products fried in unsaturated vegetable oils become rancid faster than those fried in relatively saturated oils like palm oil ( 2012) and vanaspati. Murukku, kodubale, Tengolalu, etc. are some of the popular fried snacks of south India with flours of rice and legumes as main ingredients. Flour is made into stiff dough and extruded through hand press and fried (Arya 1992). Crispness and soft texture are the desirable characteristics of these products which mostly depend on the dough composition and frying time. These fried products are gaining popularity globally because of Indian diaspora spread in various parts of the world. The products need a longer shelf life of a minimum of 2 to 3 months to cater to the needs of people in different regions. As such they have a maximum shelf life of 15 to 20 days which can be extended by process modification, selection of suitable frying medium, packaging material and form. It is observed that frying medium plays an important role in the shelf life of the product. Che-Man et al. (1999) and Sandhu et al. (2002) have studied the effect of frying media on, texture and flavour of chips. As very little information is available on the effect of frying media and packaging material on 1

2 035 Wudpecker J. Food Tech. Figure 2. Frying of Tengolalu. Figure 1. Tengolalu-a deep fat fried snack. Method of preparation shelf life of fried products, the present study was taken up. Tengolalu (Figure 1) is selected for the study as it is a relatively bland snack product with only salt and very little cumin and asafoetida as flavour ingredients which make detection of flavour deteriorations easy. The product was fried in four refined vegetable oils such as Coconut oil (CNO), Palm oil (PO), Groundnut oil (GNO) and Sunflower oil (SFO). Storage studies were conducted by packing in pouches of 75 μm polypropylene () and a laminate of 12 μm metallised polyester/50 μm High density polyethylene--low density polyethylene (Met.PET/HD-LD) under accelerated dry storage condition of 30 to 40 % RH and 38 to 40 C which minimizes the moisture transfer and restrict product deterioration mainly to rancidity development. MATERIALS AND METHODS Product Freshly prepared tengolalu using the following ingredients and method was used in the studies. Ingredients Rice and black gram flour (2:1 ratio) Butter: 15% of flour weight Salt: 2.5% of flour weight Cumin seeds: 0.25% of flour weight Asafoetida: 0.3 % of flour weight Water: 60 % of flour weight Refined oils for frying: Coconut oil (CNO) Palm oil (PO) Groundnut oil (GNO) Sunflower oil (SFO) The flour was thoroughly mixed with butter and the dough with required consistency was made using other ingredients and tengolalu was extruded directly into the pan (Figure 2) containing oil heated to 130 C using hand extruder having the plate of diameter 4.5 cm containing 5 holes of 2 mm diameter each. Frying was carried out in medium flame of domestic gas until it turned golden brown and transferred to a sieve to drain off oil. The product was cooled for about 3 hours before packing. Each tengolalu weighed about 15g. Moisture sorption studies Tengolalu was prepared using all the four oils. Known quantity of the product were taken in petri dishes and were exposed to relative humidities (RHs) ranging from 11 to 92 % built in desiccators using appropriate salt solution at 27ºC (Lopez et al., 1995). The samples were periodically weighed till they attained practically constant weight or showed signs of mould growth whichever is earlier. After equilibration, the moisture content (MC) of the product at different RHs was calculated by adding / subtracting percentage pickup/loss to/from the initial moisture content. Initial Moisture Content (IMC%) This was determined by drying known weight of the product taken in petri dish at ºC as per AACC (1983). materials 75 µm polypropylene() film and Two layer laminate of 2

3 Babu et al µm metallised polyester / 50µm High Density Polyethylene-Low Density Polyethylene (Met.PET/HD- LD) were selected for packaging and storage studies. Barrier property and compatibility of packaging material Water Vapour Transmission Rate (WVTR) and Oxygen Transmission Rate (OTR) of the packaging materials were determined as per Bureau of Indian Standard BIS (1960) and American standard for testing and materials ASTM (1982) methods respectively. The compatibility of the packaging materials for contact with fatty products was evaluated by global migration test with n-heptane at 38ºC/0.5 h as per BIS (1998) method. Fatty acid composition of oils Fatty acid methyl esters (FAME) of the oil samples were prepared by trans- esterification, according to AOCS (1998) and were analyzed on a Fisons 8000 series gas chromatograph (Fisons Co., Italy), equipped with a hydrogen flame ionization detector (FID) and a fused silica capillary column (100 m x mm i.d.), coated with 0.20 lm SP2560 (Supelco Inc., Bellefonte, PA) as the stationary phase. The oven temperature was programmed from 140 to 240º C at 4º C /min rise with an initial hold at 140ºC for 5 min. The injector and FID were at 260º C. A reference standard FAME mix (Supelco Inc.) was analyzed under the same operating conditions to determine the peak identity. The FAMEs were expressed as relative area percentage. and storage studies Six tengolalus fried in each oil weighing about 100 g were separately packed in pouches of size 21.5 x 15 cm of both the packaging materials and exposed to dry accelerated storage condition of % RH and 38-40ºC. The stored samples were withdrawn periodically every 10 days and analysed for the following physicochemical properties. AOCS (1998) by titrating the liberated iodine displaced from potassium iodide (KI) by peroxides in the fat extracted from the product against standard sodium thio sulfate solution. Free Fatty Acid (FFA) FFA expressed as % lauric acid for CNO, % palmitic acid for PO and % oleic acid for GNO and SFO was determined as per AOCS (1998) by titrating FFA present in the extracted fat against standard sodium hydroxide solution. Colour measurement Colour estimation of tengolalu (both fresh and stored samples) was carried out using Hunter colorimeter (Labscan XE, Hunterlab, Virginia) with a fixed viewing area and a light source of D65 illuminant, at an angle of 10 which was standardized to a black and white tile using Red (a +ve ) and green (a -ve ) intensity are represented on the CIE a* scale, and yellow (b +ve ) and blue (b -ve ) intensity on the CIE b* scale. The overall lightness or darkness was determined by the CIE L* value (0=black, 100=white). The total colour difference is expressed as E. The analysis was performed in duplicate (Gunther Wyszecki and Stiles WS, 2000). Texture measurement Warner-Bratzler shear force measurement of tengolalu (thickness of 0.2 cms) was done by shearing with a Warner-Bratzler shear attachment fitted with a texture measuring instrument (Model # TAHD i, Stable Microsystems, Surrey, UK) of 50 kg load cell. The individual samples were subjected to shearing at a test speed of 1mm/s and for a distance of 30 mm. The maximum force (N) from the maximum height of the force peak indicates the maximum resistance offered by the product during shearing/compression showing a major fracture on the material (Bourne, 2002). The texture measurements were repeated twice. Moisture content (MC) The MC (%) of the product was calculated by measuring the pick up or loss of the package. Peroxide value (PV) PV expressed as meq O 2 /kg fat was determined as per Sensory analysis Sensory analysis was carried out for both fresh and stored tengolalu sample. Descriptors for the product were obtained by free choice profiling, where the panelists were asked to describe the sample with as many suitable terms as possible for sensory quality of the product. The common descriptors chosen by more than 1/3 of the panelists were used for the development of a scorecard. 3

4 037 Wudpecker J. Food Tech. The panel comprised 15 trained panelists who had experience in sensory profiling of food products. Quantitative descriptive analysis (QDA) method of intensity scaling consisting of a 15 cm scale was used to evaluate the product (Stone and Sidel, 1998). The panelists were asked to mark the perceived intensity of each sensory attribute mentioned in the scorecard by drawing a vertical line on the scale with code number. The definition of each attribute of product (Ravi and Susheelamma, 2005) and the method of evaluation was explained during the initial training session. Another sensory test called rank sum analysis where a set of four samples were served to each panelist in coded porcelain plates in an individual random order. The panelists assessed the intensity of crispness and fried oil aroma quality attributes from low to high. After tasting all the samples the panelists were asked to rank the products in order of most preferred based on overall acceptability attribute. The sensory evaluation was performed in the sensory laboratory in individual booths under standard conditions ASTM (1996) by trained panelists in one session. Plain water was provided as neutralizer between samples. The results obtained with the rank sum analysis were analyzed for significance of differences between fresh and stored samples using Kramer s rank sum analysis table at p RESULTS AND DISCUSSION Product standardization A number of trials were conducted by varying rice and black gram dhal ratio and quantity of butter keeping cumin seeds and asafetida level constant with salt to. Every trial was conducted thrice and the ingredient quantity was standardised. As it can be seen from Table 1, rice and black gram dhal flour ratio of 2:1, 15 % butter, 2.5% salt, and 60 % water of flour weight has yielded a conveniently extrudable dough, crisp product with good dhal aroma. Hence the same combination of ingredients was used in the recipe for tengolalu fried in all the four oils. The absence of high flavoured spices like chilli or pepper in the product helps in easy detection of any deterioration due to oxidation/hydrolysis of fat during storage. Moisture sorption studies This study was conducted to study the nature of deterioration of the product and to fix the critical moisture content (CMC). The data on moisture content v/s RH for the product at 27 C is presented in Table 2. Sorption behaviour of the product fried in all the four oils was similar. The product with an IMC of 2.6% equilibrated to 19% RH. The product equilibrating to 11% RH was crisp but rancid odour was perceived in SFO and GNO fried samples. In others, there was some unpleasant odour even though not rancid. Tengolalu equilibrating to 22 and 32% RH with moisture contents of about 3 % were very good and comparable to fresh one even after 30 days of exposure. The product with equilibrium moisture content (EMC) of 4% under 44% RH was slightly soft but just acceptable. Those equilibrating to 56 to 75% RH with EMCs ranging between 6 and 11% were soft and unacceptable. At and above 86% RH where the EMC was above 15%, the product developed mould growth. If the product is stored at and below 19 % RH which is the ERH of the product, it loses moisture which is not good as the product is prone to auto oxidation below this moisture level. A MC of 4% and RH of 44% is critical for the product. When stored at and below this RH, the product does not lose crispness even in unpacked condition and package is needed only for hygiene, unitization, easy handling, protection against breaking during transportation and to retard the deteriorations caused by factors other than moisture. As it can be seen, moisture tolerance of the product is only 1.5 %. Also, being highly porous and nonuniform in shape, it needs a pouch of large surface area. These factors necessitate a high moisture barrier package to retain crispness which is the first step of deterioration when the product has to be stored above 44 % RH. Rancidity is the next step of deterioration which is linked with frying medium. So, it was of interest to study the rate of oxidative and hydrolytic deteriorations during storage of the product fried in different oils. Hence the storage condition of 30 to 40 % RH where moisture related deteriorations are minimum and a temperature of 38 to 40 C (accelerated dry) where chemical deteriorations are faster was selected for storage studies. Under this condition, neither mould growth nor loss of crispness will be the cause of shelf life termination. Properties of packaging materials As the RH of the storage condition is lower than the critical RH of the product, WVTR is not an important criterion to select the packaging material. Due to the large area of the pouch and high void space, large amount of oxygen is available in the headspace to cause oxidative rancidity in the product. Hence film of high oxygen barrier may not be of much use unless it is packed in inert atmosphere. Also, it is possible that during storage, the off- flavours developed in the product due to breakdown products of autooxidation cannot escape through high oxygen barrier films. This results in perception of higher degree of rancidity in high barrier films. For this reason, two packaging films viz a low oxygen barrier and a high oxygen barrier Met PET 4

5 Babu et al. 038 Table 2. Humidity-Moisture content data of Tengolalu at 27 C. Sl. No RH % EMC as is % EMC Dry wt % Remarks ± ±0.01 Good, rancid flavor in SFO and GNO fried samples ± ±0.01 Very Good ± ±0.02 Very Good ± ±0.01 Just Acceptable ± ±0.01 Soft, Not Acceptable ± ±0.01 Very soft, Not Acceptable ± ±0.01 Soggy, Not Acceptable ± ±0.01 Mould in 18 days ± ±0.01 Mould in 15 days IMC % 2.6± ±0.01 ERH % 19 CMC % CRH % 44 IMC: Initial Moisture Content; EMC: Equilibrium Moisture Content ERH: Equilibrium Relative Humidity; CMC: Critical Moisture Content CRH: Critical Relative Humidity Table 3. Properties of packaging materials used in storage study. Sl. No. material WVTR (g/m 2 /day under 90% RH gradient at 38 C) Avg of 4 Max Min readings OTR (CC/ m 2 /day/atm under 65% RH at 27 C) Avg of 3 Max Min readings Global migration values mg/dm 2 (ppm) Max Min Avg of 3 readings μm (9.7) 0.95 (9.5) 0.96 (9.6) μm Met PET/50 μm HDPE-LDPE (4.2) 0.41 (4.1) 0.42 (4.2) Limits as per BIS Specification 10 (60)IS: (60) IS: laminate were selected for the study. Nitrogen flushing was not considered as the intention was to allow deteriorations to occur so that comparison could be made among different frying oils. The compatibility of packaging materials with food is a necessary criterion for selection of packaging material. As the product is dry and contains surface fat, the packaging materials were evaluated for suitability for contact with fatty products by global migration test with n-heptane. conformed to BIS (1984) and Met.PET/HD-LD conformed to BIS (1982) specifications with the global migration values being well within the specified safety limits. The results are presented in Table 3. 5

6 039 Wudpecker J. Food Tech. Table 4. Fatty acid composition of fresh and fried vegetable oil samples (Relative area percent). Fatty acids CNO PO GNO SFO fresh oil fried oil fresh oil fried oil fresh oil fried oil fresh oil fried oil C8:0, Caprylic acid 6.2± ±0.05 ND ND ND ND ND ND C10:0, Capric 4.5± ±0.1 acid 0 ND 0.2±0.01 ND 0.3±0.01 ND ND C12:0, Lauric acid 50.1± ± ± ±0.3 ND 0.6± ±0 0.5±0.01 C14:0, Myristic acid 21.4± ± ± ± ± ± ± ±0.05 C14:1, Myristoleic acid ND ND ND 0.2±0.01 ND 0.2±0.01 ND 0.4±0.01 C16:0, 13.1± 9.4±01. Palmitic acid ± ± ± ± ±0.1 10±0.2 C16:1, palmitoleic ND 0.1±0.01 ND ND ND 0.2±0.01 ND 0.3±0.01 acid C18:0, Stearicacid 1.3± ± ± ± ± ± ± ±0.05 C18:1, Oleic acid 5.6± ± ± ± ± ± ± ±0.3 C18:2, linoleic acid 1.3± ± ± ± ± ± ± ±0.6 C18:3, lenolenic acid ND ND ND ND 0.6± ±0.01 ND ND C20:0, arachidic acid ND 0.5±0.01 ND 0.6± ± ±0.01 ND ND C22:0, Behenic acid ND ND ND ND 3.3± ± ±0.01 ND TOTAL S F A (%) MUFA (%) PUFA (%) S:M:P RATIO 1:0.06:0.01 1:0.11: :0.67: :0.71: :2.38: :1.88: :2.27: :1.54:3. 52 *CNO Coconut oil; *PO-Palm oil; *GNO-Groundnut oil;*so-sunflower oil *S F A Saturated Fatty Acids; M U F A Mono Unsaturated Fatty acid; P U F A Poly Unsaturated Fatty acid., ND: Not detected Table 5. Chemical quality of vegetable oils before and after frying. SI. NO Oil Fresh oil Fried oil PV a FFA b PV a FFA b 1 CNO 0.00± ± ± ± PO 1.9 ± ± ± ± GNO 1.4± ± ± ± SFO 1.1± ± ± ±0.04 a meq. Of O 2 /kg fat b % oleic acid/palmitic acid/lauric acid Table 6. Quality variations observed in freshly prepared Tengolalu. Product Color Hardness as L* a* b* ΔE Maximum force (N) Darkest one 47.1± ± ± ± ±1.2 Lightest one 62.3± ± ± ± ±0.8 6

7 Babu et al. 040 Fatty acid composition of oils Generally, refined vegetable oils are used for frying. 4 different refined oils, CNO, GNO, PO and SFO which were used for frying tengolalu had different fatty acid compositions. The stability of the oil during frying depends upon the % age of unsaturated fatty acids. The oils were observed for the fatty acid compositions before and after frying. The oil in which change in fatty acid composition is minimum is more stable and can be expected to give better shelf life of the product. As it can be observed from Table 4, the saturated fatty acid content of fresh CNO, PO, GNO and SFO were 93.1, 54.8, 20.6 and 10.3 % respectively and mono unsaturated contents respectively were 5.6, 36.8, 49.0 and 23.4 % in the order of GNO>PO>SFO>CNO. The oils that contain more PUFA are highly reactive with oxygen at high temperature of frying and expected to decrease after frying. It is evident from the Table 4 that the changes in fatty acid compositions in SFO and GNO are predominant. The loss of PUFA was more than 13 % in SFO and GNO oils after frying and the changes were marginal in case of CNO and PO. Stability of oils depends upon the PUFA content, which was less in CNO followed by PO, GNO and SFO. Thus fats with unstable acids are expected to have lesser shelf life with respect to oxidative rancidity. The saturated fatty acid content increased from 21 to 26 % and 10 to 16 % in case of GNO and SFO respectively after frying. This is expected due to the oxidation of PUFA during frying at high temperature. The linoleic acid content decreased from 29.8 to 25.7 % in GNO and from 66.3 to 57.7 % in SFO after frying. There was only marginal change in mono unsaturated fatty acid. But in case of CNO, there was a decrease in saturated fatty acid content from 93 % to 89 % while mono unsaturated fatty acids increased from 6 to 10 % after frying. There was hardly any change in the fatty acid composition of PO after frying. Thus, the results indicate that PO is most stable among the four oils studied and expected to offer longer shelf life for the product. FFA of around 0.3. This may be due to the butter used in the product and also the moisture coming out of the dough at the elevated temperatures. Product quality As the product was fried manually, wide variation was observed in colour and texture of the product. Therefore, the difference between colour and texture of the lightest and darkest product was measured (Table 6). The dark ones were hard whereas, the light ones were crisp and porous. This textural difference continued even after the products attained the same moisture content after equilibration among themselves. The colour and texture of the stored sample falling between the maximum and minimum values observed for the fresh sample were considered same as that of fresh. Storage studies The changes in chemical and sensory quality of tengolalu monitored during storage studies are as follows: Moisture changes Moisture content of the product packed in both the packaging materials remained almost the same throughout the study (Tables 7 to 10). The ERH of the product at 27 C is 19% and the storage atmosphere is 30 to 40 % with a gradient of only 11 to 21% between the packed product and storage atmosphere. This gradient further reduces at C. This restricts moisture ingress into the package. Owing to good moisture barrier property of packaging materials, moisture permeability was practically zero. The selection of packaging materials and storage conditions are thus justified as there is no gain in the moisture content of the product. Quality changes of oils after frying As evidenced from table 5, quality of all the four oils deteriorated after frying. The results indicate that the quality of fresh oil is very good with PV and FFA ranging between 0 and 1.9 and 0 and 0.21 respectively for different oils. Generally, during frying, rate of oxidation of oils is more at elevated temperatures. Thus PV increased to 3.4 to 30.0 for different oils which are in commensuration with the degree of unsaturation of oils. Increase in FFA is also expected due to hydrolysis of oils. Irrespective of the initial FFA, all fried oils showed PV changes As it can be seen from Table 7, PV changes in CNO fried Tengolalu is only from 1.5 to 4.6 in and 4.2 in met PET film during 60 days of storage. This is due to the less oxygen susceptibility of CNO due to its high degree of saturation. Change in PV of PO fried tengolalu was 6.5 to 10.6 in and 6.5 to 10.2 in met PET film (Table 8). In case of GNO the change was from 8.95 to in and to in Met. PET film (Table 9). In all these three oils the PV changes were almost the same in both the packaging materials. It indicates that the rate of oxidation is so slow that higher oxygen permeability in film has 7

8 041 Wudpecker J. Food Tech. Table 7. Physico-chemical changes in Tengolalu fried in coconut oil during storage. Material HDPE- LDPE Storage Moisture Color Hardness as Period Content PV a FFA b Maximum L* a* b* E (Days) (%) force(n) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±2.6 60# 2.52± ± ± ± ± ± ± ±1.8 # off- note was not observed even after 60 days a meq. of O 2/kg fat, b % oleic acid/palmitic acid/lauric acid Table 8. Physico chemical changes in Tengolalu fried in palm oil during storage. Material HDPE- LDPE Color Hardness as Storage Moisture Period Content PV a FFA b Maximum L* a* b* E (Days) (%) force(n) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.37 Analysis discontinued due to rancidity development ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.42 Analysis discontinued due to rancidity development a meq. of O 2/kg fat, b % oleic acid/palmitic acid/lauric acid Table 9. Physico-chemical changes in Tengolalu fried in groundnut oil during storage Material HDPE- LDPE Storage Moisture Color Hardness as Period Content PV a FFA b Maximum L* a* b* E (Days) (%) force (N) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.61 Analysis discontinued due to rancidity development ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±2.0 8

9 Table 9 contd. Babu et al ± ± ± ± ± ± ± ± ±0.21 a meq. of O2/kg fat, b % oleic acid/palmitic acid/lauric acid Analysis discontinued due to rancidity development Table 10. Physico-chemical changes inttengolalu fried in sunflower oil during storage. Material HDPE- LDPE Storage Moisture Color Hardness as period Content PV a FFA b Maximum force L* a* b* E (Days) (%) (N) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.02 Analysis discontinued due to rancidity development ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0..13 Analysis discontinued due to rancidity development ± ± ±0.41 a meq. of O 2/kg fat, b % oleic acid/palmitic acid/lauric acid no effect. As head space oxygen is utilised by the product, it creates a partial pressure differential between head space of the pack and the atmosphere. Since this pressure gradient is less, oxygen permeation takes place at a slow rate. As head space gas is the same in both pouches, change in PV is similar in both packages with marginal increase in than met PET film in GNO. This change is more pronounced in tengolalu fried in SFO where the change in PV was from 17.5 to about 600 in and from 17.5 to in Met PET film (Table 10). Therefore, in case of products fried in oils with high PUFA, the rate of autoxidation is influenced by oxygen permeability of packaging material. Partial vacuum was created in the pouches containing tengolalu fried in SFO indicating utilisation of all head space oxygen within 20 days thereby creating a gradient giving scope for more permeability of oxygen through package. This caused further increase in PV. FFA changes FFA value of tengolalu changed from 0.35 to 0.98 (0.89) in CNO (Table 7), 0.7 to 2.55(2.0) in PO (Table 8), 0.32 to 3.19 (2.9) in GNO (Table 9) and 0.41 to 4.9(4.55) in SFO (Table 10) packed in (Met. PET film) respectively in 60 days. Generally, FFA changes will be more in oils with higher saturated fatty acids. As per that, the increase in FFA should be in the order of CNO> PO> GNO> SFO. However, the results have indicated that FFA increase is in the order of SFO>GNO>PO>CNO. This may be due to breakdown of peroxides and formation of short chain fatty acids and not due to oleic acid in case of SFO and GNO. FFA of freshly fried products was more than that of their respective oils after frying. This could be due to the contribution from ingredients like butter, rice and black gram dhal flour used in the preparation of tengolalu. Colour and texture As it can be seen from Tables 7 to 10, there are no significant changes for colour with frying media, storage period and packaging material. All data fall within the fluctuations due to time and temperature of frying as reported in Table 6. There is not much difference in moisture content between the fresh and stored samples as packaging materials and oil media did not affect moisture transfer from or to the product. Hence no major difference was observed in maximum force indicating no changes in texture. Values of colour during storage also fall within the range of those caused by variations in frying. The lower magnitudes of maximum force during 9

10 043 Wudpecker J. Food Tech. Table 11. Mean sensory scores of stored Tengolalu fried in coconut oil. material HDPE-LDPE Storage period (Days) Creamish color Surface uniformity Hardness Gritty Crispy Oily mouth feel Cereal/ Legume Fried oil aroma Salty Asafoetida Overall quality 0 5.6± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.9 60* 5.3± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.7 Table 12. Mean sensory scores of stored Tengolalu fried in palm oil. Pakkg. material HDPE- LDPE Storage period (Days) Creamish Color Surface uniformity Hardness Gritty Crispy Oily mouth feel Cereal/ Legume Fried Oil aroma Salty Asafoetida Overall quality 0 7.7± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Off -note or rancid flavor observed in this withdrawal and analysis discontinued ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Off- note or rancid flavor observed in this withdrawal and analysis discontinued 10

11 Babu et al. 044 Table 13. Mean sensory scores of stored Tengolalu fried in groundnut oil. Material HDPE-LDPE Storage period (Days) Creamish color Surface uniformity Hardness Gritty Crispy Oily mouth feel Cereal/ Legume Fried oil aroma Salty Asafoetida Overall quality 0 6.7± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Off- note or rancid flavor observed in this withdrawal and analysis discontinued ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Off- note or rancid flavor observed in this withdrawal and analysis discontinued Table 14. Mean sensory scores of stored Tengolalu fried in sunflower oil. Material HDPE-LDPE Storage period (Days) Creamish color Surface uniformity Hardness Gritty Crispy Oily mouth feel Cereal/ Legume Fried oil aroma Salty Asafoetida Overall quality 0 6.8± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Off- note or rancid flavor observed in this withdrawal and analysis discontinued ± ± ± ± ± ± ± ± ± ± ± Off note or rancid flavor observed in this withdrawal and analysis discontinued storage as compared to fresh sample indicate that the product offered less resistance and was compressed elastically up to a small strain level until showing a fracture on the outer boundary to create a fracture (Bourne, 2002). When the strain was further increased, the materials failed by disintegrating into two pieces (Ravi et al., 2007). However, differences were noticed among different frying media with respect to maximum force. Freshly fried samples from refined CNO, GNO and SFO showed maximum force of N as compared to those fried in PO (14.9 N). But interestingly, samples fried in CNO had maintained the crispness till the end of storage period unlike other samples (Tables 7 to 10 and 11). Sensory analysis As it can be seen form Figure 3 and Figure 4, offnote was not observed even by 60 days in CNO and 50 days in PO fried samples respectively. On 60 th day the product fried in PO were clearly rancid. The products fried in GNO and SFO were clearly rancid by the end of 30 days and 20 days respectively (Figure 5 and Figure 6). This indicates a shelf life of >60 days, 50 days, 20 to 30 days and 10 to 20 days for the products fried in CNO, PO, GNO and SFO, respectively. Otherwise, no significant difference was noticed for all other sensory attributes which may be mainly due to no change in moisture contents of the product. Moisture content will be responsible for crispness, grittiness, surface uniformity and to some extent creamish colour. Salty and asafetida 11

12 045 Wudpecker J. Food Tech. Met.PET/HDPE-LDPE HDPE-LDPE Figure 3: Sensory profile of stored Tengolalu fried in coconut oil. Figure 5. Sensory profile of stored Tengolalu fried in groundnut oil. HDPE-LDPE HDPE-LDPE Figure 4. Sensory profile of stored Tengolalu fried in palm oil. s are not expected to change with storage. The possible reason for colour changes as discussed earlier may be due to little variation in frying temperature or time and not due to storage period. Instrumental colour and texture analysis correlate with sensory analysis results. As there was no change in moisture content, changes in instrumental texture in terms of crispness, hardness and Figure 6. Sensory profile of stored Tengolalu fried in sunflower oil. surface uniformity was not observed sensorial also. The negative attributes like fried oil aroma was mentioned however stale and rancid, bitter after were not found in the fresh samples. When they were found rancid, it was so predominant that sensory analysis for that sample 12

13 Babu et al. 046 was felt unnecessary. Rank sum analysis The results of rank sum analysis of the product fried in four different oils and two packaging materials are presented in Table 11 and 12. The rank sum results analysis based on Kramer s rank sum table show that there is marginal difference (significant at p 0.05) among products fried in different media but not between packaging materials. Fresh product fried in GNO received highest rank based on crispness and overall quality. The panelists felt marginally less fried oil aroma in GNO fried sample, which might have been the reason to judge GNO fried samples as marginally superior. This may be due to their preference for GNO as most of the panelists were commonly GNO users in respect of Indian snack foods. Otherwise there is no significant difference in fresh samples fried in different oils. However due to oxidative rancidity during storage, SFO had lowest shelf life of < 20 days and CNO had maximum shelf life of >60 days. As expected, shelf life decreased with increase in PUFA content of the oil (Table 4). Shelf life of the products will be in the ratio of CNO: PO:SFO: GO:: >4.0: 3.0: 1.5:1.0. Hydrolytic rancidity expected to occur in product fried in CNO was not observed till 60 days, which may be due to slow reaction between oil - water interface as the product remained at its initial moisture content throughout the study. The effect of moisture content on crispness was studied by sorption studies, but its effect on hydrolytic rancidity was not studied as oxidative rancidity occurs faster and is rate determining step for shelf life after moisture. Thus, viewed from both physico-chemical and sensory parameters together, sensory quality depended on the frying media and storage time. The PUFA content of the oil played an important role in the shelf life of the fried product. Sunflower oil with highest PUFA has yielded less than 20 days shelf life where as CNO with lowest PUFA has offered more than 60 days shelf life. GNO and PO have given 30 days and 50 days shelf life respectively. When the products turned clearly rancid, PVs were 10.6 for PO, 24.6 for GNO and 100 for SFO (Table 8 to 10), but they were very good when PV was 9.1, 16.2 and 36.4 respectively. This is in line with BIS recommendation for palm oil which specifies max permissible PV as 10 and above this value, the oil tends to be clearly rancid. Mahadeviah et al. (1993) observed perceivable rancidity after a PV of 20 in GNO. In another spicy snack food kodubale PV crossed the maximum limit of 10 by 20 th day by which time rancidity was observed (Kumar et al., 1993). Thus for all the four oils, PV correlates with PUFA content as well as sensory quality of the product. FFA increased with storage time but no correlation between sensory quality and FFA could be seen (Tables 7-10). Even the product fried in CNO did not show any hydrolytic rancidity by the end of 60 days of storage. In other oils where shelf life was terminated due to rancidity, oxidation was the cause. Conclusion Storage studies were conducted to see the effect of frying media on the shelf life of tengolalu, a traditional South Indian snack. The study revealed that the product fried in oil with higher PUFA content is more prone to oxidative rancidity and will have shorter shelf life. Even though FFA values increased with storage time, they did not reveal any hydrolytic rancidity throughout the study. It can be concluded that shelf life of tengolalu and allied fried products in 4 different oils studied would be in the ratio of CNO: PO: SFO: GO: >4.0: 3.0: 1.5:1.0. In case of air packing, barrier property of packaging materials has no pronounced effect on shelf life of tengolalu as head space oxygen available is sufficient to spoil the product. REFERENCES AACC (1983). Approved methods of the American Association of Cereal chemists, 8 th Edm. Vol. I, Minnesota USA. American Oil Chemists Society, AOCS (1998). Official methods, Ca 5a-40, Cd 8-53 and Ce 1-62, 5 th Ed, Champaign, IL. Arya SS (1992). Convenience foods emerging scenario. Indian food industry, 11(4): American Society for Testing and Materials ASTM (1982) D-1434, Philadelphia, Penn., USA. American Society for Testing and Materials ASTM (1996). Sensory testing method. 2 nd Edn. ASTM manual 26(E. Chamber IV and M. B. Wolf, Eds). ASTM. West Conshohocken, P. A, pp Bureau of Indian Standards, BIS (1998). Methods of analysis for the determination of specific and or overall migration of constituents of plastic material and articles intended to come contact with foodstuffs Methods of analysis, IS: 9845, New Delhi, India. Bureau of Indian Standards BIS (1960). Methods of sampling and testing for papers and allied products, IS: 1060, Part II, New Delhi, India. Bureau of Indian Standards, BIS (1984). 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