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Open AccessArticle

Advantages of Liquid Nitrogen Quick Freezing Combine Gradient Slow Thawing for Quality Preserving of Blueberry

1
Sericulture & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences, Key Laboratory of Functional Foods, Ministry of Agriculture and Rural Affairs, Guangdong Key Laboratory of Agricultural Products Processing, Guangzhou 510610, China
2
College of Food Science, South China Agriculture University, Guangzhou 510642, China
3
College of Food Science and Technology, Zhongkai University of Agriculture Engineering, Guangzhou 510225, China
*
Authors to whom correspondence should be addressed.
Crystals 2020, 10(5), 368; https://doi.org/10.3390/cryst10050368
Received: 12 March 2020 / Revised: 27 April 2020 / Accepted: 29 April 2020 / Published: 4 May 2020
(This article belongs to the Special Issue Ice Crystals (Volume II))
Berries are perishable fruits with high nutritional value. Freezing is an effective way for food preservation. Freezing and thawing methods play key roles in preserving edible values and commodity values of food. This study investigated the effects of spray liquid nitrogen quick freezing (NF−20~−100 °C) and gradient thawing on the physical and functional characteristics of blueberries by using immersion and refrigerator freezing and microwave, ultrasonic, room- and low-temperature, and static-water thawing as comparisons. The results show that NF−80 °C freezing combined with −20~−5~4 °C. gradient thawing can retain more than 95% of polyphenols and other nutritional compounds (including pectin, soluble sugar, and vitamin C) in thawed blueberries compared with fresh blueberries. Besides, this method shows the best results in preserving the hardness, cell structure, and water distribution of blueberries. It is also revealed that the ultralow temperature (−100 °C) freezing does not bring a significant advantage in preserving blueberries. Rapid thawing methods such as microwave and ultrasound thawing are not suitable for blueberries, which might be due to their small size and thin skin. The results suggested that the combination of NF−80 °C freezing and −20~−5~4 °C gradient thawing is the optimal process for blueberry preservation. The outcomes of this study will serve as theoretical guidance for improving the industrial process for freezing and thawing blueberries. View Full-Text
Keywords: liquid nitrogen quick freezing (NF); gradient thawing; blueberry; quality liquid nitrogen quick freezing (NF); gradient thawing; blueberry; quality
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MDPI and ACS Style

Cheng, L.; Wu, W.; An, K.; Xu, Y.; Yu, Y.; Wen, J.; Wu, J.; Zou, Y.; Liu, H.; Zhu, J.; Xiao, G. Advantages of Liquid Nitrogen Quick Freezing Combine Gradient Slow Thawing for Quality Preserving of Blueberry. Crystals 2020, 10, 368.

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