Analysis of the quality attributes of osmotically dehydrated mango

摘要

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 Keith) 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°C and 45, 55 and 65 °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.