Abstract
A comparative study was conducted on the effect of vacuum impregnation and drying methods on the production of dried sweet potatoes with high bioactivity. The present study determined the quality and physicochemical properties of dried sweet potato depending on the used impregnating solutions. Sweet potatoes were pretreated in freshly squeezed onion (O) and kale (K) juice, onion and kale (OK) mixture (1:1), and sodium chloride solution. Vacuum impregnation (VI) was carried out under reduced pressure (6 kPa) for 2 min, after which the impregnating solution was dispensed and maintained under vacuum for 4 min. Sweet potato slices were dried using vacuum drying (VD) and freeze drying (FD) methods. Higher content of polyphenols, carotenoids, and chlorophyll, as well as increased antioxidant capacity and higher VOC profile, were recorded for the dried products obtained using the sublimation method. The use of vacuum impregnation reduced the hardness of the products and other textural characteristics, such as cohesiveness, springiness, and gumminess. Furthermore, we found that vacuum impregnation pretreatment was a beneficial method for improving the characteristics of dried vegetables. The highest content of phenolics, carotenoids, and chlorophylls in dried sweet potatoes were recorded when samples were impregnated with onion and kale juice. For the fresh sweet potato, the highest contribution in VOC composition had phenylacetaldehyde (44.90%), (E)-2-octen-1-al (9.43%), and benzaldehyde (8.18%), respectively. The interesting content of VOC profile compounds in dried sweet potatoes was recorded when samples were impregnated with kale juice.
Highlights
Dried fruits and vegetables have become more and more popular as healthy snacks, replacing, to some extent, potato chips or crisps [1].Drying reduces the growth of micro-organisms and inhibits enzymatic degradation, extending the time of consumption of fruits and vegetables
Samples subjected to vacuum drying (VD) were characterized by an average of 3% lower total phenolic (TP) content compared to the freeze drying (FD) samples; these differences were not statistically significant
Dried products obtained by the FD method showed higher con-tents of polyphenols, carotenoids, chlorophyll, antioxidant capacity, and Volatile Organic Compounds (VOCs) composition, as well as the lowest values of hardness, cohesiveness, springiness, and gumminess
Summary
Drying reduces the growth of micro-organisms and inhibits enzymatic degradation, extending the time of consumption of fruits and vegetables. Freeze drying (FD) involves removing water from a frozen product through ice sublimation, which is the conversion of ice to vapor, bypassing the liquid state. It is a complex and multi-stage process [4] that ensures optimum product quality [5]. Dried products obtained by this method showed levels of polyphenolic compounds and antioxidant activity that were comparable to those of the raw material [9]. The low temperature of the FD process slows the degradation reactions of bioactive compounds and preserves higher nutrient values compared to other drying methods [2]
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