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Precautions for Pineapple Freeze Drying
2026-04-23
Raw material pretreatment: Anti browning and enzyme removal Pineapple contains a large amount of polyphenol oxidase, which is easily oxidized and discolored by direct freeze-drying; Simultaneously containing bromelain, improper handling can cause "mouth irritation". Maturity selection: It is recommended to choose pineapples that are 8-9% ripe and have a strong aroma. Raw pineapples are sour and have coarse fibers, while overripe pineapples are prone to softening, rotting, and collapsing during quick freezing. Peeling and eye removal: The outer skin and fruit eyes must be completely removed. The fiber in the fruit core (hard core) is relatively thick, and it is recommended to cut or slice it into extremely thin pieces to avoid affecting the crispy taste. Blanching enzyme inactivation (key step): In order to prevent the finished product from oxidizing and blackening, and reduce the activity of bromelain (reducing the tingling sensation when consumed), it is recommended to blanch the sliced pineapple in hot water at 80 ℃ -90 ℃ for a moment. Blanching can also have a sterilizing effect, but the time should not be too long to avoid boiling the fruit pulp. Color protection treatment: If the color requirements are extremely high, a small amount of citric acid or vitamin C solution can be used to soak and protect the color after blanching. Vacuum drying: Temperature control to prevent "moisture regain" is the most prone stage to problems. The high sugar content of pineapple makes it highly hygroscopic and has a low melting point. Vacuum degree control: The vacuum degree inside the chamber should be kept at a low level (such as 10-30 Pa) to ensure smooth sublimation of ice crystals. Temperature control (core difficulty): Slow heating: Due to the high sugar content of pineapple, its eutectic point (glass transition temperature) is relatively low. The temperature of the heating plate needs to be slowly increased (recommended rate 0.5-1.5 ℃/hour), and the material temperature must not exceed its eutectic point, otherwise the surface of the pineapple slices will melt, become sticky, and even exhibit a "sugar flow" phenomenon. Preventing coking: Although heating is necessary, excessive temperature can cause Maillard reaction in high sugar pineapple, resulting in darker and bitter color of the finished product. Analysis of drying: In the later stage, it is necessary to increase the temperature appropriately (such as to 20 ℃ -30 ℃) to remove bound water and ensure that the final moisture content is reduced to 1% -5%. If the moisture content is too high, dried pineapple will become tough, not crispy, and easily moldy.
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