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

doi:10.3969/j.issn.1000-2561.2022.03.021

Abstract

Abstract:

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.

Key words: litchi, fruit, drying, blanching, sulfur-free color-protecting

CLC Number:

TS255.36

GAO Zhiqiang, SHEN Xiajun, LIN Yuzhao, ZENG Lingzhen, LIN Hetong. Technologies of Blanching and Sulfur-free Color-protecting in Litchi Fruit During Drying Processing[J]. Chinese Journal of Tropical Crops, 2022, 43(3): 614-621.

Figures/Tables 11

References 23

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水平 Level	(A)柠檬酸 Citric acid	(B)NaCl Sodium chloride	(C)抗坏血酸 Ascorbic acid
1	0.1	1.0	0.1
2	0.2	1.5	0.2
3	0.3	2.0	0.3

水平 Level	(A)柠檬酸 Citric acid	(B)NaCl Sodium chloride	(C)抗坏血酸 Ascorbic acid
1	0.1	1.0	0.1
2	0.2	1.5	0.2
3	0.3	2.0	0.3

试验号 Test number	(A) 热烫温度 Blanching temperature/℃	(B) 柠檬酸浓度 Citric acid concentration/%	(C) 热烫时 Blanching time/min	(D) 空列 Empty column	PPO活性 PPO activity/ (U·mg^-1)
1	1(90)	1(0.1)	1(1)	1	0.73
2	1	2(0.2)	2(2)	2	0.57
3	1	3(0.3)	3(3)	3	0.47
4	2(95)	1	2	3	0.33
5	2	2	3	1	0.12
6	2	3	1	2	0.30
7	3(100)	1	3	2	0.18
8	3	2	1	3	0.41
9	3	3	2	1	0.30
K₁	1.77	1.24	1.44	1.15	∑=3.41
K₂	0.75	1.10	1.20	1.05
K₃	0.89	1.07	0.77	1.21
k₁	0.590	0.413	0.480	0.383
k₂	0.250	0.367	0.400	0.350
k₃	0.297	0.357	0.257	0.403
极差R	0.340	0.056	0.223	0.050
主次顺序			A>C>B
优水平			A₂B₃C₃

试验号 Test number	(A) 热烫温度 Blanching temperature/℃	(B) 柠檬酸浓度 Citric acid concentration/%	(C) 热烫时 Blanching time/min	(D) 空列 Empty column	PPO活性 PPO activity/ (U·mg^-1)
1	1(90)	1(0.1)	1(1)	1	0.73
2	1	2(0.2)	2(2)	2	0.57
3	1	3(0.3)	3(3)	3	0.47
4	2(95)	1	2	3	0.33
5	2	2	3	1	0.12
6	2	3	1	2	0.30
7	3(100)	1	3	2	0.18
8	3	2	1	3	0.41
9	3	3	2	1	0.30
K₁	1.77	1.24	1.44	1.15	∑=3.41
K₂	0.75	1.10	1.20	1.05
K₃	0.89	1.07	0.77	1.21
k₁	0.590	0.413	0.480	0.383
k₂	0.250	0.367	0.400	0.350
k₃	0.297	0.357	0.257	0.403
极差R	0.340	0.056	0.223	0.050
主次顺序			A>C>B
优水平			A₂B₃C₃

变异来源 Variation source	平方和 Sum of squares	自由度 df	均方 Mean square	F值 F value	F₀	显著性 Significance
(A)热烫温度	0.204	2	0.102	51.000	F_0.05(2,2) = 19.000	*
(B)柠檬酸浓度	0.006	2	0.003	1.500	F_0.01(2,2) = 99.000
(C)热烫时间	0.077	2	0.039	19.500		*
误差	0.004	2	0.002
总变异	0.291	8