Quick-frozen grapes are made from fresh grapes through a series of processing to make quick-frozen products, which can maintain the original flavor, color and nutrition of grapes. Fast-frozen grapes prolong the storage period of grapes, facilitate long-distance transportation and meet consumer demand in different regions and seasons. Quick-frozen grapes can also be used as dessert ingredients for high-end hotels and restaurants, or for cold summer dining.
l Materials and methods
1.1 Materials
Red Globe grapes are collected from the Yangling area of ​​Shaanxi.
1.2 Equipment
Electronic balance, handheld juicer, hand-held sugar meter, Haier temperature-controlled refrigerator, Haier temperature-controlled freezer, vacuum sealing machine and so on.
1.3 Methods
1.3.1 Process flow: raw materials → threshing, picking → cleaning, draining → disinfection, rinsing, draining → color protection, draining → pre-cooling → quick freezing → packaging, frozen storage
1.3.2 Operation points: The raw materials are free of pests, no scars, no mechanical damage, good coloring, full, fruity grape spikes; threshing, require scissors cut one by one, do not injure the grape fruit, and reject the unqualified fruit Granules; Wash, drain, rinse the cut grape fruit 5 to 6 times with tap water, wash until no impurities, drain water; disinfect, rinse, drain, disinfect the raw materials to extend the shelf life, completely immerse the grapes in preparation In a good 0.05% potassium permanganate solution, keep for 5 minutes, then rinse with tap water for 5-6 times, then drain; protect color, drain, impregnate raw materials to inhibit enzyme activity, control oxidation, prevent browning, Place the sterilized grapes in a suitable coloring solution, soak for a few minutes, remove and allow to drain; pre-cool, drain the grapes into a 2 °C freezer and pre-cool for 15 hours until the temperature drops. To O ~ 5 °C, pre-cooling can shorten the freezing time and protect the raw materials, the pre-cooling of the final temperature closer to the raw material freezing temperature is better, the higher the final temperature may lead to cracking during quick freezing, pre-cooling time can not be too long, To prevent loss of water and shrinkage, quick-freeze, the pre-cooled grapes are laid flat in a large plate, placed in a -40°C freezer to freeze for 30 minutes, and the freezing speed requires a maximum ice crystal generation area within 30 minutes, and the frozen product core temperature reaches -18°C. Below °C, quick-frozen products are required to be non-adhesive; packaging, frozen storage, quickly frozen grapes into the packaging bag, packaging with vacuum packaging machine, in order to prevent the enzymes during the storage process and other physical and chemical effects on the product The negative effects must be frozen at -18°C and kept as constant as possible.
1.3.3 Measurement indicators and methods: weightlessness rate = (preliminary weight ~ final weight) / initial weight x 100% (The weight before freezing is the initial weight, and the weight after thawing is the final weight at each measurement)
Soluble solids (SSC): hand-held sugar meter determination;
Titratable acid: titration method;
Sensory evaluation: Evaluation of product color, flavor, and organization.
2 Results and Analysis
2.1 Influence of Raw Material Treatment on Products
The effect of the fruit on the product. After processing, the weight loss rate of grapes without fruit pedicles was significantly higher than those with fruit pedicles, indicating that the sap of products processed from grapes without fruit pedicles was seriously lost. In addition, the contents of soluble solids and titratable acids are both low and the loss of nutrients is serious, and the sensory indexes such as color and texture are not as good as that of grapes with fruit pedicles. Therefore, this experiment uses a method with a fruit pedicle for threshing, and the fruit pedicle retains about 2mn.
2.2 The effect of different color protection agents on the product
The effect of color protectors on the product. From the color point of view, with 0.1% VC solution color protection effect is best, 1% NaCl solution color protection effect is the second, 0.1% citric acid solution color protection effect is the worst. From the weight loss rate, the weight loss rate with the 0.1% VC solution is the lowest, while the weight loss rate with 0.1% citric acid is the highest. The three groups of products have the same soluble solids content. Although the titratable acid content of the product protected with 0.1% VC solution was lower, it was the closest to the content of the raw material. It can be seen that the high titratable acid content of the other two sets of products was due to the loss of juice. , 0.1% VC solution as a color protection agent both color protection, but also to maintain the loss of grape nutrients less. Therefore, 0.1% VC solution was chosen as a color-protecting agent in this test.
2.3 The effect of different packaging on storage quality
2.3.1 Effect of Different Packaging on Soluble Solids Content in Product Storage
The content of soluble solids in the products packed in vacuum bags increases slowly over time. This indicates that the quality of the products in the vacuum bags is almost unchanged during the storage period, there is no loss of juice, and only a small amount of water evaporates, making bags There was a slight increase in the soluble solids content of the inner product, and there was little change in the soluble solids content of the products packed in ordinary bags during storage. Therefore, the quality of the product in the vacuum bag is better than the quality of the product in the common bag.
2.3.2 Effect of different packaging on titratable acid content during product storage
The titratable acid content of products packed in vacuum bags decreases first and then increases with the passage of time. This is because the product has a small amount of loss of titratable acid in the early stage of storage due to the loss of water, and it is due to the concentration phenomenon during the later period of storage. Appeared, its titratable acid content increased significantly. The products packed in ordinary bags first decrease sharply and then increase slowly during storage. This is due to the loss of juice resulting in acid content in the product, in the later due to reduced soluble solids content of the product, the relative increase in acid content. In contrast, the acid content of the product in the vacuum bag is higher than the acid content of the product in the common bag.
2.3.3 Effect of different packaging on weight loss rate during storage
The weight-loss rate of products packed in vacuum bags tends to increase slowly during storage, while the products packaged in common bags change significantly during storage, with a larger increase. This shows that the airtightness of the ordinary bag is significantly worse than that of the vacuum bag, which not only causes the water in the bag to evaporate faster but also has air in the bag. In this way, the product in the bag reacts with oxygen in the air, resulting in loss of juice, soft texture, loss of nutrients, browning and other undesirable consequences.
2.3.4 Effect of Different Packaging Bags on Sensory Quality during Product Storage
During the storage period, the sensory quality of the product in the vacuum bag remained basically unchanged, its color was rosy and uniform, and its sweet and sour taste was palatable with a rich fruit aroma. Until the late period, there was no significant change in color, the texture was slightly softened, and the fruity aroma was reduced, but the sweet and sour taste was palatable. On the other hand, the appearance quality of products in ordinary bags has changed significantly. At the beginning of storage, there is a clear fading phenomenon. After 15 days of storage, some of the fruit was browned. Although the flavor did not change significantly, the texture became soft and the juice was seriously lost. Near the end of the storage period, almost all of the fruit was browned, with little fruit and odor.
Based on the above four aspects, it can be seen that vacuum bag packaging is better than ordinary bags. The vacuum bag effectively maintains the color, aroma, taste and inherent nutrition of the product while the ordinary bag does not provide a basic protection. Therefore, this test chose a vacuum bag as a packaging bag.
3 Conclusion
Keep 2mm grape pedicles, the best frozen effect. Choosing 0.1% VC solution for color protection can effectively prevent grape browning. The vacuum bag was selected as the package bag for the frozen grape product.
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