荔枝果实干制加工的热烫和无硫护色工艺

荔枝是我国南方一种重要的热带、亚热带水果,具有较高的营养价值和商业潜力.然而,在高温高湿季节,采后荔枝果实极易发生腐烂变质、果皮褐变、病原菌侵染等品质劣变现象.因此,荔枝果实除鲜食外,常被加工成不同的商业产品,特别是荔枝果干.干制荔枝由于干制加工时间较长,易发生果皮褐变,导致其外观色泽、产品质量和风味丧失,最终限制荔枝...

Technologies of Blanching and Sulfur-free Color-protecting in Litchi Fruit During Drying Processing

Litchi fruit, with the high nutritive value and commercial potential, is an important tropical and subtropical fruit in south China. However, the harvested litchi fruit is prone to quality deterioration such as rot occurrence, pericarp browning and pathogen infection in high temperature and high humidity seasons. Thus, litchi fruit is often processed into different commercial products in addition to fresh-eating, especially dried litchi. Due to the long drying processing time, the dried litchi is highly susceptible to serious pericarp browning development, resulting in the loss of appearance color, product quality and fruit flavor of the dried litchi, and eventually limit the sustainable development of litchi processing industry. Therefore, it is necessary to develop a safe and effective drying processing technology for the dried litchi fruit to delay pericarp browning, stabilize appearance color and improve quality of the dried litchi fruit. Some studies reported that the technologies of blanching and sulfur-free color protection liquids could effectively control the occurrence of enzymatic browning during drying processing by inactivating the activity of polyphenol oxidase (PPO), and thus improve the product quality of the dried horticultural products. However, there are few reports on delaying pericarp browning development and maintaining appearance quality in the dried litchi during hot-air drying processing by using the safe color-protecting technology. Therefore, in this study, in order to control the pericarp browning of litchi fruit during hot-air drying, the technologies of blanching and sulfur-free color-protecting in litchi fruit during drying processing were studied. An L₉(3⁴) orthogonal experimental design was used to investigate the effects of different blanching conditions such as blanching temperature and blanching time with different concentration of citric acid, and different sulfur-free color protection liquids including citric acid, sodium chloride (NaCl) and ascorbic acid, on the inactivation of PPO in the pericarp of litchi fruit, which would help to obtain the optimal parameters of blanching and sulfur-free color-protecting in litchi fruit during drying processing. The results displayed that the blanching temperature 95℃, blanching time 3 min and 0.3% citric acid were the optimum blanching conditions for dried litchi fruit during processing. Additionally, the application of the sulfur-free color protection liquids including 0.2% citric acid, 2.0% NaCl and 0.3% ascorbic acid for litchis revealed the best color-protecting of dried litchis. The data indicated that the above optimized parameters could effectively suppress the occurrence of pericarp browning in litchi fruit during drying processing, and thus maintain the better quality of dried litchi fruit.