Analysis of the quality attributes of osmotically dehydrated mango

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1 Analysis of the quality attributes of osmotically dehydrated mango Maida han a, Lília Ahrné b and Jorge Oliveira c a Universidade Eduardo Mondlane, Maputo,Mozambique (maida.khan@uem.mz) Lília Ahrné, SI, Gothenborg, Sweden (Lilia.Ahrne@sik.se) Jorge Oliveira, University College Cork, Cork, Ireland (jmfcoliveira@gmail.com) ABSTRACT The effect of osmotic dehydration (OD) conditions on quality parameters of mango were studied against the natural variability (white noise) and variation across two different varieties and harvest years. Colour and texture parameters and water activity of mango pieces before and after osmotic dehydration at constant temperature and osmotic solution concentration were measured for several samples at six different processing times, for 3 batches of mangoes. Two were from the same harvest year and different varieties (Haden and eith) while the third was from the Haden variety but a different harvest year. All three batches were processed at 9 different combinations of temperature (T) and osmotic solution concentration (SSC), according to a full factorial design at 3 levels (30, 40 and 50 o C and 45, 55 and 65 o Brix). The third was processed for 6 different fixed set times, while the first two were processed for different sampling times, predicted by a kinetic model at each set of conditions so that each data point collected would have the same water content in the 9 different processing conditions. This sampling design would enable to remove the effect of water content in the analysis of the quality parameters between different treatments. It was experimentally verified that indeed the model predictive ability was excellent, and the effect of temperature and solution concentration could therefore be tested for similar water contents (78.6, 75.2, 71.8, 68.4 and 65%). The results showed that at any set of conditions of T and SSC none of the quality parameters varied with statistical significance throughout the OD process, except water activity. Although some parameters suggested a general tendency of evolution, this was less than the variability between replicates. The frequency distribution analysis of more than 150 different measures of the quality parameters of the fresh mango showed a close to normal distribution in all cases except firmness, where the distribution was tailed for all 3 batches. Differences between the two varieties of the same harvest year were not statistically significant, while those between the same variety in different harvest years were. The differences could be related to a likely different stage of maturity of the fruits in the different years at the same time of the year, possibly due to different weather growing conditions, and imply that either variety is equally suitable for processing. It was also found that OD processing had little effect on the spread (standard deviation) of the values around the average for the colour parameters, but the spread decreased significantly with processing for firmness and water activity, which means that the OD processing makes the mango pieces more homogeneous between themselves while affecting colour and firmness minimally and lowering water activity. eywords: mango, osmotic dehydration, quality (;) INTRODUCTION Drying is one of the most widely used methods to preserve fruits. However, the quality of dehydrated products is often poor. Collapse of the structure, discoloration and tough texture are common quality problems. Not less important, although not visually perceived, is loss of flavour and nutritional value. Moreover, some dried products are intended for rehydration, and their rehydration capacity and the quality of rehydrated products are often poor. Osmotic dehydration has been reported to be useful prior to drying to produce a variety of shelf-stable dried products with improved quality attributes such as colour, texture and aroma (Heng et al., 1990). Foods are diverse, complex and active systems, in which microbiological and biochemical changes take place simultaneously. Food preservation is dependent on colour, texture and water activity and those are the quality

2 parameters that are widely used to evaluate the quality of food. Colour is usually the first attribute that the consumer observes (Saenz et al., 1993). From the consumption point of view, firmness and taste are also important quality parameters. From the shelf life and safety point of view, the presence of moisture expressed as water activity is the most important parameter that has a strong effect on deteriorative reactions. Water activity is the parameter that relates more closely to microbial growth and biochemical changes, and is therefore the usual measure needed to assess the shelf life of the product and it has become a very useful tool in dealing with water relations of foods during processing. The objective of this work was to assess the influence of osmotic dehydration and its operating conditions on the quality factors of mangoes. The parameters measured relate to colour, firmness and water activity. MATERIALS & METHODS Two varieties of mango from two different harvest years were used: Haden 1 (2004) and Haden 2 (2005) variety and eith variety (2005). Both Haden 2 and eith were used for the quality analysis and the initial quality of raw material samples was evaluated before each osmotic dehydration experiment in terms of moisture content, total soluble solids, colour, firmness and water activity. The osmotic dehydration experiments with Haden 1 were done up to 240 minutes. Samples were collected after 20,40, 60, 120 and 240 min, and the quality was analysed for the initial and final product. The osmotic dehydration experiments with Haden 2 and eith were done up to a moisture content of 65% (g O/g product). The sampling times and the time needed to reach a moisture content of about 65% in the osmotically dehydrated product were predicted using the model developed by han et al (2008). In this way, the quality measurements were taken for samples of similar water content, to isolate the effect of water content on the quality parameters. The predicted sampling and final times are presented in Table 1. Table 1. Sampling times predicted by the model developed han et al (2008) to provide the water content indicated on the first column X w predicted T SSC t (min) T SSC t (min) T SSC t (min) ( o C) ( o Brix) ( o C) ( o Brix) ( o C) ( o Brix) After each sampling time, the quality of the products was analysed in terms of colour, firmness and water activity, and the kinetics of quality change evaluated for all different processing conditions. The final quality characteristics of the osmotic dehydrated mango products obtained under different processing conditions could therefore be compared with all samples having approximately 65% water content. Visual colour measurement, CIE L*a*b*values, were determined with a Minolta chromameter (Model CR-10). Water activity was determined using a Decagon Aqualab device, CX 2 STE. Moisture content was determined according to the AOAC, Method Soluble solids concentration was determined from the measurement of the o Brix of the sample, and Firmness (penetration force) was determined by measuring the maximum force required for a 3 mm probe to penetrate the mango cylinder held perpendicular to the probe, to a depth of 10 mm at 50 mm/s using an Instron texture analyser. The results were expressed as maximum compression force at puncture.

3 RESULTS & DISCUSSION Quality characteristics of the raw material The quality of fruits and vegetables is strongly dependent on harvest, cultivars, climate, soil type and ripeness. This results in a wide variability of the product characteristics, which makes it difficult to analyse the changes in quality during processing of plant foods. The raw material presents a high variability, being the firmness the most variable parameter. The average quality parameters values for all mangoes used are presented in the Tables 2 Table 2 Average initial firmness, water activity, composition and colour parameters of the Haden 1(H 1 ), Haden 2( ) and eith () fresh mangoes F a w X w X ss L a b H ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±4.4 The firmness of Haden 2 and eith were very similar and much higher than the firmness of Haden 1. There are two reasons that can be behind this result. Haden 1 and Haden 2, although they are from the same variety, were from different seasons (years). These results suggest that the Haden 1 mangoes were used in a much more mature stage compared to the Haden 2 and eith. The fact that the firmness was lower together with the higher yellowness value of Haden 2 can be related to the degree of ripeness. Mango is a climacteric fruit, which can be harvested in mature stage and continues the ripening process off the plant (Holdsworth, 1979). During ripening, colour development occurs, together with fruit softening and characteristic flavour development. The mango flesh tends to become softer and more yellow. It can therefore be concluded that in 2004 the fruits matured much faster in the tree than in 2005, possibly due to the differences in the weather patterns, as other growth factors were the same. The moisture content values of fresh samples were 82± 1 % for Haden 1, 78±2 % for Haden 2 and 80±2. The soluble solids fraction ranged from 0.14 ±0.02 to 0.17±0.01 being the highest value for Haden 1, and the water activity was 0.991± and 0.989±0.003 for Haden 1 and Haden 2, respectively, and 0.988±0.003 for eith. All batches were therefore statistically similar regarding these parameters. The frequency distributions were all approximately normal, except for the soluble solids content of the eith variety and the water activity of Haden 1. The colour parameters confirmed the yellowness of the edible part of mangoes. The values obtained were closed to the maximum possible yellowness value (L-value), which is 80 (Zarubica et al., 2005). Comparing the three mango batches, Lightness (L), ranged from 64.2±4.4 to 73.3±3.4. The lowest lightness was for Haden 1. The redness was higher for Haden 1 than for Haden 2 and eith, which were more similar. Yellowness in many fruits is related to the ripening as during the ripening process, colour development occurs and the ripen fruits are usually characterized in many fruits by their yellowness. Correlating a and b (redness and yellowness) and L and b (yellowness and Lightness), it can be observed that mangoes of different variety eith and Haden 2, but from the same season, had more similar characteristics than Haden 1 and Haden 2 from the same variety different season (Figure 1).

4 H 1 20 H 1 Redness (a) Redness (a) Figure 1. Correlation between a and b values and L and b values It appears that the effect of the harvest year on colour was more important than the variety of mangoes used. It can be concluded that product homogeneity can be controlled by the state of ripeness, with both varieties being equally suitable. Although there is a high variability in the initial data, the distribution appeared to be normal for all colour parameters. Firmness was the most variable quality parameter in fresh mango. The Haden 1 mangoes were much softer compared to Haden 2. The maximum compression force was similar for the Haden 2 and eith batches. The distribution was clearly not normal, but tailed (it was fitted by the Weibull model). Basically, Haden 2 and eith, from 2005, showed a proportion of harder pieces that were not present in Haden 1, of 2004, that therefore was more homogeneous. It can be concluded that sample homogeneity would recommend selecting samples in a good mature state. Effect of osmotic dehydration on the quality characteristics of OD mango pieces Evaluation of quality during processing time 0 None of the quality parameters showed any statistically significant kinetic effect, except water activity (as expected, its lowering is the purpose of OD). Figure 2. Some examples of the evolution of water activity with processing time Comparison between initial and final values of relevant quality parameters Figs 3 show just the initial and final values of some relevant quality factors. For the quality parameters studied there are no statistically significant differences, except for water activity. It follows that for all parameters (except a w ) all end products, obtained at the 9 different conditions, all with different processing times but approximately 65% water content, can be pooled together, and the effect of OD can be analyzed globally, with no influence of the processing conditions. It can however be noted that the water activity is much more consistent for Haden 2 and eith batches, for the obvious reason that the water content of the samples in this case was the same, while with Haden 1 the

5 process time was fixed at 240 min. Therefore, samples in that case had different water contents and hence water activities. This shows that setting the process using the model is far better than fixing a process time, in order to ensure consistency. 1,000 Haden 1 Initial Haden 1 Final 1 Haden 2 Initial Haden 2 Final 1 eith Initial eith Final 0,980 0,98 0,98 Water activity (aw) 0,960 0,940 Water activity (aw) 0,96 0,94 Water activity (aw) 0,96 0,94 0,920 0,92 0,92 0,900 0,9 0, Figure 3. Initial and final water activity values at all processing conditions The firmness is reported in the literature to be lost during OD processing. Loss of firmness in apricot halves subjected to OD for 2 hours at room temperature was ascertain by Forni et al. (1986). Monsalve-Gonzalez (1993) found that at early stages of OD processing softening of apples have occurred while a decrease in firmness followed by a later increase back to the original texture have been observed by Bolin & Huxol (1993). There is an unclear behaviour of the structure of food products during osmotic dehydration. In this study the osmotic dehydration of mango up to 65% moisture content appears to not affect the firmness of the product. There are probably changes that the fruits undergo differently during OD processing. The structural characteristic, the ripening stage and the composition of the fruit may have an effect on the solid-liquids exchange in and consequently on the final product quality. Analysis of the variability of OD processed mango The final colour quality of the osmotic dehydrated mango Haden 2 and eith were very similar compared to Haden1 as can be seen in Figure 4. The figure also shows the initial average for a better visualisation of the influence of OD (albeit not statistically significant, as the figure also allows verifying). The higher yellowness of Haden 1 was even slightly enhanced by the OD process, making it even more different from the other 2 batches Redness (a) H 1 Lightness (L) H Figure 4. Correlation between a and b values and L and b values for OD processed samples of mango with 65% water content. Symbols without bars indicate the average of the initial fresh mango pieces Table 3 show the results of the mangoes processed at the 9 different conditions of temperature and solution concentration for the required time to reach approximately 65% water content. This results shows that there are no statistically significant differences due to the OD process, except for water activity. However, it is very interesting to note that although the standard deviations were high for both fresh and processed mango in most of the quality parameters, the variability was smaller in the OD processed products. It can be concluded that OD does not affect the quality parameters significantly, but makes the product more homogeneous than in fresh.

6 Table 3. Average firmness, water activity, composition and colour parameters of the Haden 2 and eith OD mangoes a w X w X ss L a b E F F 0.988± ± ± ± ±5.9 N/a 5.17±4.47 OD 0.973± ± ± ± ± ± ± ±3.65 F 0.989± ± ± ± ± ±4.4 N/a 5.67±3.87 OD 0.976± ± ± ± ± ± ± ±3.31 F =Haden 2 fresh ; OD = Haden 2 OD processed to 65% water conten; F = eith Fresh; OD =eith OD processed to 65% water content CONCLUSION The eith and Haden varieties are very similar both in terms of their colour, texture and water activity parameters as fresh, and after osmotic dehydration, with no statistically significant differences between them. However, there were significant differences between Haden batches of two successive years, 2004 and It was concluded that this was due to a difference in the ripening and maturation times in the two years, and better product homogeneity is achieved with products that are fully mature. Osmotic dehydration did not affect colour nor texture significantly. Although some tendencies could be observed, these were smaller than the variability between replicates. However, osmotic dehydration significantly reduced the spread of texture and water activity, that is, it resulted in a more homogenous product. REFERENCES [1]Bolin, H.R. & Huxsoll, C.C Partial drying of cut pears to improve freeze/thaw texture. Journal of Food Science, 58, [2]Forni, E. Torregiani, D. Battiston, P & Polesello, A Research into changes of pectic substances in apricots and peaches processed by osmotic dehydration. Carbohydrate polymers, 6, [3] Heng, ; Guilbert, S; Cuq, J.L.1990 Osmotic dehydration of papaya - influence of process variables on the product quality. Sciences des aliments.10, 4, [4] Holdsworth, S.D Fruits. In: Priestley R. J. (Eds). Effects of heating in Food stuffs. London: Applied Science Publishers Ltd. pp [5] han,mam, Ahrné,L, Oliveira, JC and Oliveira, FAR Prediction of water and soluble solids concentration during osmotic dehydration of mango, Food and Bioproducts Processing, Volume 86, Issue 1, March 2008, Pages 7-13 [6] Saenz, C., Sepulveda, E., Araya, E., & Calvo, C Colour changes in concentrated juices of prickly pear Opuntia ficus indica during storage at different temperatures. Lebensmittel-Wissens chaft und Technologie,26, [7] Torregiani, D., Forni, E., Maestrelli, A. & Quadri, F Influence of osmotic dehydatration and pectic composition of kiwifruit slices. Drying Technology, 17: (7&8), [8] Zarubica, A. R., Miljkovic, M. N., Purenovic, M. M., Tomic, V. B Colour parameters,whiteness indices and physical features of marking paints for horizontal signalization, Facta Universitatis,Series: Physics, Chemistry and Technology,. 3; 2,