Nigerian Food Journal Official Journal of Nigerian Institute of Food Science and Technology NIFOJ Vol. 32 No. 1, pages 133 138, 2014 www.nifst.org Shelf Life Extension of Toasted Groundnuts through the Application of Cassava Starch and Soy Protein-Based Edible Coating *Chinma, C.E. 1, Ariahu, C.C. 2 and Abu, J.O. 2 ABSTRACT The use of cassava starch and soy protein concentrate edible coatings containing 20% glycerol in extending the shelf life of toasted groundnut during ambient (27 ± 1 o C) storage for 14 days was studied. Chemical indices of oxidative rancidity and sensory parameters were evaluated using standard procedures. Moisture uptake, peroxide and thiobarbituric acid values of uncoated groundnuts were higher than 100% cassava starch coated groundnuts while toasted groundnuts coated with 50:50 (cassava starch:soy protein concentrate) had the lowest values. Toasted groundnuts coated with 50:50 (Cassava starch:soy protein concentrate) film had higher colour, taste, texture and overall acceptability scores than toasted groundnuts coated with 100% cassava starch film and control. The use of 50:50 (cassava starch:soy protein concentrate) edible coatings on toasted groundnut extended the shelf life of toasted groundnuts for 14 days compared to uncoated toasted groundnuts which developed objectionable taste after second day of storage at ambient (27 ± 1 o C) condition. Keywords: Cassava starch, soy protein concentrate, edible film, toasted groundnuts, shelf life extension. Introduction Toasted groundnut is a widely consumed form of groundnut in Nigeria, which can be consumed alone or combined with dry toasted maize (popcorn), garri, coconut, bread or plantain (Bankole et al., 2005). Toasted groundnuts like other forms of groundnuts are rich in protein, fat, minerals and vitamins, and have crispy texture and nutty flavour. Nuts are prone to the development of oxidative off-flavour because of their high polyunsaturated lipid content (Yazdani et al., 2006). According to Riveros et al. (2013), synthetic antioxidants such as butylated hydroxyanisole 1 Department of Food Science and Technology, Federal University of Technology, Minna, Nigeria 2 Department of Food Science and Technology, University of Agriculture, Makurdi, Nigeria * corresponding author: chinmachiemela@yahoo.com (BHA), butylated hydroxytoluene (BHT) and propyl gallate (PG), are used in many foods to prevent rancidity, and their health safety remains questionable. Also, the antioxidant effect of natural antioxidants such as essential oils are not enough in many cases in decreasing deterioration and shelf life extension of nuts (Olmedo et al., 2008; Silva et al., 2010; Riveros et al., 2013). On the other hand, synthetic polymers used as food packages tend to react with food materials releasing naptha-based compounds which may be carcinogenic on ingestion by humans (Parra et al. 2004) and contribute to environmental pollution (Arvanitoyannis et al.,1996; Krochta and De Mulder-Johnston, 1997). Edible films and coatings are innovations within biodegradable active packaging concept, which can improve safety and/or functional or sensory
134 Nigerian Food Journal Vol. 32 No. 1, 2014... Full Length Article properties while maintaining the quality of food packaging (Parra et al., 2004; Riveros et al., 2013). Cassava starch coatings have been applied in fruits such as mango and pineapple in order to extend their shelf while preserving quality (Chiumarelli et al., 2010; Bierhals et al., 2011). To date, there is paucity of information on the use of coatings prepared from blends of cassava starch and soy protein concentrate in preserving the quality of textured foods such as toasted groundnuts. Edible films have been successfully produced using cassava starch and soybean protein concentrates (Chinma et al., 2012). In that study, results obtained showed that addition of up to 20% glycerol level improved the sensory, mechanical and water vapour permeability properties of cassava starchsoy protein concentrate edible films compared to 100% cassava edible film. Also, the results indicated that 50:50 cassava starch:soy protein edible films have improved mechanical and low water vapour permeability value and could therefore find application as coatings in textured foods. This forms the thrust of this study on the use of cassava starch-soy protein concentrate edible coatings in preserving the quality attributes of toasted groundnuts. Materials and Methods Source of raw material Fresh sweet cassava (TMS 30470) tubers and soybean (TGX 1448-2E) seeds were procured from Crop Production Department, Federal University of Technology, Minna, Nigeria. Cassava starch extraction, preparation of soy protein concentrate and edible coatings Cassava starch extraction and soy protein concentrate were prepared as reported by Chinma et al. (2012). Film forming solutions were prepared from cassava starch and soy protein concentrate (100:0 and 50:50) containing 20% glycerol as described by Chinma et al., (2012). Glycerol concentration of 20% was weighed and dissolved into distilled water, followed by the addition of composite blends to obtain film forming suspension in which starch concentration was 5% (w/w) of overall water content independent of plasticizer concentration. The ph of the film forming suspension was adjusted to 9.98 (with 1 M NaOH) using a ph meter (DELTA 320). The film forming suspension was heated in a heating flask in a hot plate over 90 C for 5 min with continuous stirring using a glass rod to obtain the film forming solution. Coating of toasted groundnuts Dipping method as described by Chien et al. (2007) was adopted for coating of toasted groundnut. Toasted groundnuts were dipped into film forming solution for about 15 sec. The coated samples were taken out from the solution with a slotted spoon and then put on an aluminum foil to allow excess coating material to drain from the product. Coated samples were allowed to dry under fan for 1 min. The samples were treated by dipping 3 times to ensure a uniformity of coating on the surfaces. Coated and un-coated toasted groundnuts were stored at ambient condition (27±1 o C) for 14 days. They were analyzed for chemical and sensory properties at intervals of 2 days. Performance evaluation of edible coatings The moisture content and peroxide value of coated and uncoated toasted groundnuts were determined according to the method described by AOAC (1995) while thiobarbituric acid value was determined as described by Pearson (1981). Sensory evaluation A twenty-member trained panel was used for sensory evaluation of coated and uncoated toasted groundnuts. Sensory evaluation was carried out for two weeks at intervals of two days. The coded samples were randomly presented to sensory panel in white plastic plates. Coated and uncoated toasted groundnuts were evaluated for colour, taste, texture and overall acceptability while fresh toasted groundnuts were used as standard. Each sensory attribute was rated on a 9-point hedonic scale (where 1 = disliked extremely while 9 = liked extremely).
Shelf Life Extension of Toasted Groundnuts through the Application of Cassava Starch... Chinma et al. 135 Statistical analysis Data were analyzed by analysis of variance (Steel and Torrie, 1980). The difference between mean values was determined by least significant difference (LSD) test. Significance was accepted at 5% probability level. Results and Discussion Effect of edible coatings on moisture content, peroxide and thiobarbituric acid values of toasted groundnuts stored at 27±1 o C. The effect of cassava starch-soy protein concentrate edible coatings on the moisture content, peroxide value and thiobarbituric acid value of toasted groundnut stored at 27±1 o C is presented in Table 1. The moisture content, peroxide and thiobarbituric acid value increased with storage time. The moisture uptake in uncoated toasted groundnuts was higher (9.22 to 24.54%) than toasted groundnuts (9.22 to 18.56%) coated with cassava starch-soy protein concentrate. Among the coated samples, toasted groundnuts coated with 50:50 (cassava starch:soy Table 1: Effect of edible coatings prepared from blends of cassava starch and soy protein concentrate on the moisture, peroxide value and thiobarbituric acid value content of toasted groundnut during storage at 27±1 o C Blend ratio Moisture (%) Uncoated toasted Storage period (days) 0 2 4 6 8 10 12 14 groundnut 9.22 a + 0.78 11.22 a + 0.78 13.38 a + 0.44 16.47 a + 0.41 19.25 a + 0.54 21.13 a + 0.05 23.13 a + 0.05 24.54 a + 0.54 100CS:0SPC 9.22 a + 0.52 9.92 b + 0.52 11.84 b +0.95 13.61 b + 0.38 14.90 b + 0.80 15.88 b + 0.01 17.09 b + 0.01 18.56 b + 0.90 50CS:50SPC 9.00 a + 0.11 9.46 b +0.11 10.39 c +0.33 11.04 c + 0.80 12.29 c + 0.23 13.51 e +0.01 14.40 c +0.01 15.79 c + 0.32 Peroxide value (Meq/kg) Uncoated toasted groundnut 0.31 a + 0.78 0.75 a + 0.78 1.38a + 0.44 2.47 a + 0.41 3.84 a + 0.54 5.13 a + 0.05 8.60 a + 0.05 11.54 a + 0.54 100CS:0SPC 0.29 a + 0.52 0.31 b + 0.52 0.59 b + 0.95 0.81 b + 0.38 1.24 b + 0.80 1.61 b + 0.01 1.79 b + 0.01 2.40 b + 0.90 50CS:50SPC 0.27 a + 0.11 0.27 b + 0.11 0.31 b + 0.33 0.58 b + 0.80 0.73 c + 0.23 0.98 c + 0.01 1.24 b + 0.01 1.53 c + 0.32 Thiobarbituric acid value (mg N/100g sample) Uncoated toasted Groundnut 0.10 a + 0.01 0.19 a + 0.00 0.43 a + 0.01 0.97 a + 0.03 1.23 a + 0.05 1.96 a + 0.03 2.51 a + 0.01 3.02 a + 0.15 100CS:0SPC 0.10 a + 0.00 0.12 a + 0.00 0.22 a + 0.01 0.27 b + 0.02 0.58 b + 0.02 0.76 b + 0.20 0.92 b + 0.04 1.07 b + 0.01 50CS:50SPC 0.10 a + 0.00 0.10 a + 0.00 0.15 a + 0.00 0.22 b + 0.01 0.31 b + 0.02 0.36 b + 0.05 0.45 b + 0.03 0.57 c +0.03 Values are mean and standard deviation of three determinations. Values in a column with different superscript for a given parameter are significantly (p < 0.05). 100 CS:0 SPC = 100% cassava starch edible coating 50 CS:50 SPC = 50% cassava starch: 50% soy protein concentrate edible coating
136 Nigerian Food Journal Vol. 32 No. 1, 2014... Full Length Article protein concentrate) had lower moisture content than 90:10 (cassava starch : soy protein concentrate) coating. Kranner and Karel (1990) reported that moisture has an accelerating effect in the initial (incipient) oxidation of lipid. The low moisture content of toasted groundnuts coated with 50:50 (cassava starch: soy protein concentrate) than 100% cassava starch coatings may be attributed to low water vapour permeability value or barrier effect of the former than latter. This was in line with our previous report (Chinma et al., 2012) that edible films prepared from cassava starch and soy protein concentrate blends had low water vapour permeability than 100% biofilms due to increased formation of dense matrix. Table 2: Effect of edible coatings prepared from blends of cassava starch and soy protein concentrate on the colour, taste and texture of toasted groundnut during storage at 27 ± 1 o C Blend Ratio 2 4 6 8 10 12 14 Colour Uncoated toasted groundnut 7.85 a + 0.03 6.25 a + 0.12 4.88 b + 0.04 4.45 b + 0.13 3.83 c + 0.10 3.50 b + 0.02 2.89 b + 0.01 100 CS:0 SPC 7.94 a + 0.10 7.81 a + 0.16 7.60 a + 0.13 7.57 a + 0.06 7.74 a + 0.02 6.62 a + 0.01 6.07 a + 0.01 50 CS:50 SPC 7.96 a + 0.09 7.57 a + 0.10 7.36 a + 0.09 7.12 a + 0.05 6.55 b + 0.19 6.17 a + 0.03 4.89 b + 0.01 Taste Uncoated toasted groundnut 5.31 b + 0.01 ND ND ND ND ND 5.47 a + 0.03 100 CS:0 SPC 7.40 a + 0.00 6.67 a + 0.06 6.33 a + 0.80 5.86 a + 0.03 5.51 a + 0.06 5.43 a + 0.01 5.36 ab + 0.01 50CS:50SPC 7.55 a + 0.02 7.03 a + 0.05 6.85 a + 0.00 5.02 a + 0.01 4.83 a + 0.02 4.30 b + 0.01 4.89 b +0.01 Texture Uncoated toasted groundnut 5.95 b + 0.00 5.58 b + 0.05 4.55 b + 0.03 3.60 c + 0.00 3.01 b + 0.00 2.86 c + 0.01 2.20 c + 0.00 100CS:0SPC 7.48 a + 0.06 7.01 a + 0.02 6.83 a + 0.01 6.22 a + 0.05 5.94 a + 0.00 5.72 a + 0.01 5.39 a + 0.00 50CS:50SPC 7.04 a + 0.00 6.58 a + 0.02 6.11 a + 0.01 5.26 b + 0.01 4.90 a + 0.01 4.04 b + 0.00 3.65 b + 0.01 Values are mean and standard deviation of three determinations. Values followed by different superscript in a column for a given parameter are significantly (p < 0.05) different from each other. 100CS:0 SPC = 100% cassava starch edible coating 50CS:50 SPC = 50% cassava starch: 50% soy protein concentrate edible coating ND = Not Determined Oxidative deterioration has often been quantified in terms of peroxide value or/and thiobarbituric acid value (Pranoto et al., 2009). Peroxide and thiobarbituric acid values of toasted groundnut samples increased with increase in storage time. Peroxide and thiobarbituric acid values of uncoated toasted groundnuts were higher than those of coated groundnuts. Among the coated samples, toasted groundnuts coated with 50:50 (cassava starch:soy protein concentrate) had lower peroxide and thiobarbituric acid values than toasted groundnuts coated with 100% cassava starch. The increase in peroxide and thiobarbituric acid values of coated and uncoated toasted groundnuts during storage may be due to moisture uptake or increased activities of lipolytic enzymes.. The peroxide and thiobarbituric acid values of coated toasted groundnuts were below the acceptable level of 10 Meqv/kg and 1.0 Meq/kg respectively, for foods
Shelf Life Extension of Toasted Groundnuts through the Application of Cassava Starch... Chinma et al. 137 containing fat (AOAC, 1995) throughout the storage period while the uncoated samples were above the acceptable limits from eight day of storage (although there were indications of objectionable taste after the second day of storage). This implies that cassava starch-soy protein concentrate films were effective in delaying oxidative deterioration in toasted groundnuts during ambient storage. However, the low peroxide and thiobarbituric acid values of toasted groundnuts coated with 50:50 (cassava starch:soy protein concentrate) than 100% cassava starch coatings may be attributed to low moisture sorption characteristics of the former than the latter due to its strong barrier effect (Chinma et al., 2013). Mate et al. (1996) reported that whey protein isolate/glycerol edible coatings delayed oxidative deteroriation in toasted peanuts. Effect of edible coatings on sensory properties of toasted groundnuts stored at 27 ± 1 o C The effect of cassava starch-soy protein concentrate edible coatings on the colour, taste, texture and overall acceptability of toasted groundnuts stored at 27 ± 1 o C is presented in Tables 2 and 3 respectively. The colour, taste, texture and overall acceptability of coated and uncoated toasted groundnuts decreased with storage time. However, toasted groundnuts coated with 50:50 (Cassava starch:soy protein concentrate) film had higher colour, taste, texture and overall acceptability scores than toasted groundnuts coated with 100% cassava starch film and control. The coated toasted groundnuts were acceptable throughout the storage period while the uncoated toasted groundnuts developed objectionable taste after the second day of storage (Table 3). Colour and texture Table 3: Effect of edible coatings prepared from blends of cassava starch and soy protein concentrate on the overall acceptability of toasted groundnuts during storage at 27 ±1 o C Blend ratio Storage period (days) 2 4 6 8 10 12 14 Uncoated toasted groundnut 5.47 b + 0.22 2.19 b + 0.06 ND ND ND ND ND 100 CS:0 SPC 7.56 a + 0.14 7.29 a + 0.18 6.74 a + 0.09 6.25 a + 0.05 5.68 b + 0.02 4.92 a + 0.06 4.63 a + 0.04 50CS:50SPC 7.48 a + 0.12 7.03 a + 0.17 6.44 a + 0.14 6.36 a + 0.01 6.19 a + 0.00 5.30 a + 0.00 5.13 a + 0.01 Values are mean and standard deviation of three determinations. Mean values in a column with different superscript are significantly (p < 0.05). 100 CS:0 SPC = 100% cassava starch edible coating 50 CS:50 SPC = 50% cassava starch: 50% soy proteins concentrate edible coating ND = Not Determined change during storage of toasted nuts is one of the major determinants of consumer acceptability. In addition to consumer acceptability, colour is also used for quality control (Trezza and Krochta, 2000; Kahyaoglu and Kaya, 2006). Texture is another important quality determinant of toasted nuts that characterizes crispiness and crunchiness (Szczesniak 1990; Wilkinson et al., 2000). Differences in the sensory attributes between the coated samples and non-coated controls could be attributed to the barrier effect caused by cassava starch-soy protein concentrate coating. The reduction in sensory scores of uncoated groundnuts with storage time could be attributed to onset of rancidity. These observations in sensory attributes were consistent with earlier reports by Javanmard (2008) who reported that coating of food materials improved their colour, flavour, crunchiness and overall acceptability.
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