Mechanism of Browning Occurring during the Processing of Semi-dried Persimmons

Abstract

To investigate the mechanism of browning occurring during the processing of semi-dried 'Atago' persimmon (Diospyros kaki Thunb.) fruit, the changes in several components related to enzymatic and non-enzymatic browning were determined. The browning of semi-dried persimmons developed when the water content of fruit decreased to about 50% or less, and hand massage (HM) treatment promoted both the drying process and development of browning. The polyphenol content as a substrate of polyphenol oxidase (PPO) markedly decreased during the first 7 days of drying before the occurrence of browning. PPO activity gradually decreased and was lower in dry + HM than dry treatment alone during drying. The ascorbic acid (AsA) content decreased and HM accelerated the reduction by 7 days of drying. Dehydroascorbic acid (DHA) also decreased with stagnation in the mid-stage during 14 days of drying and was lower in dry + HM than dry treatment alone during the latter period of drying. Furfural, a non-oxidative degradation product of AsA, started to increase from 4 or 10 days of drying in dry + HM or dry treatment, respectively. Reducing sugars, fructose and glucose, markedly increased for the first 4 days with a concomitant decrease in the sucrose content, and were higher in dry + HM than dry treatment. The content of amino acids gradually decreased, and no difference was observed between treatments. Hydroxymethylfurfural (HMF), as an intermediate product from fructose to brown pigments, decreased during drying and was lower in dry + HM than dry treatment alone. These results suggest that the oxidative and nonoxidative degradation of AsA would contribute markedly to the browning of semi-dried persimmon fruit, and enzymatic browning by PPO and the Maillard reaction between amino acids and reducing sugars might not play an important role.

Changes in the Physico-Chemical Properties of Persimmon (<i>Diospyros kaki </i>Thunb.) During Drying and Quality Deterioration During Storage

“…However, technological advances have allowed this drying method to be improved, with hot-air cabinet drying, solar drying, oven and vacuum oven drying, microwave drying, and freeze-drying having been tested in recent years (Karakasova et al, 2013;Kursun and Karaca, 2018). Each of these drying methods has a different effect on the physico-chemical properties of the final product, as do parameters such as the persimmon cultivar, pre-treatment, drying temperature, air flow rate, humidity around the fruit, and drying period (Ayuko et al, 2017;Demiray and Tulek, 2017;Karakasova et al, 2013;Yamada et al, 2009). An overview of studies on the effect of drying process on the physico-chemical properties of dried persimmon was shown in Table 2.…”

“…Studies have shown that the sucrose content of persimmon fruit disappears approximately 10 days after the beginning of sun drying, whereas the fructose and glucose contents initially decrease and then increase during the drying process due to the decomposition of sucrose (Yamada et al, 2009). Total sugars make up approximately 60% of the dry matter throughout the drying process (Ishii and Yamanishi, 1982), while the ratios of glucose to fructose are generally 1.3-1.4 in the raw flesh, 1.2 in over-mature flesh, and 1.0-1.42 in dried flesh (Hirai and Yamazaki, 1984).…”

“…Oxidative and non-oxidative degradation of ascorbic acid contributed to the browning of samples. Yamada et al, 2009 Dipping in 3% potassium metabisulphite solution (15min); 3% critic acid (15 and 35 min respectively).…”

“…With the best combination ratios, the evaluation of color change revealed a decreasing tendency in the value of △E during the drying period. Kim et al, 2018 In an investigation of the mechanism that causes browning to occur during the processing of semi-dried persimmon, Yamada et al (2009) observed changes in several components that are related to both enzymatic and non-enzymatic browning and found that browning develops when the water content of the fruit decreases to 50% or less. It has also been shown that "hand massage" treatment may promote the development of browning (Kawaguchi et al, 2012;Yamada et al, 2009).…”

“…The drying process increases the carbohydrate, dietary fiber, and nutrient and phytochemical contents of persimmon, while causing a loss of vitamins (Table 1), all of which contribute to the palatability, taste, color, nutritive, and consumption attributes of the dried product (Arnal and del Río, 2004;Celik and Ercisli, 2007). In addition, the drying process causes softening of the fruit (Kim et al, 2014), as well as moisture evaporation, sugar crystal formation on the surface, and gelled pectin formation, the level of each of which varies between different treatments and affects the quality of the final product (Nicoleti et al, 2007;Sugiura and Taira, 2008;Yamada, et al, 2009). The effects of the drying process on the quality of dried persimmon in terms of properties such as the viscoelasticity, sugar content, color, white powder formation on the surface, astringency, membrane formation on the surface, and presence of bioactive compounds have previously been described (Hayashi, 1989a;Ishii and Yamanishi, 1982;Karakasova et al, 2013;Manabe et al, 1978;Nicoleti et al, 2005;Park et al, 2006;Tulek and Demiray, 2014), knowledge of which is also important for understanding the storage behaviors.…”