Effects of Pretreatment Methods on the Quality of Frozen Strawberries by Blast Freezing and Immersion Freezing
| Autor: | 張君瑜 |
|---|---|
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 The growing season of strawberry is very short, if use freezing technology to preserved strawberries, it can be used in the off season. But ice crystals formed during freezing causes damage to the structure of strawberries, thus loss in quality. Three pretreatments have been studied in this research : the vacuum infusion process with different concentrations of calcium solutions (calcium chloride and calcium lactate), different concentrations of sugar solutions (sucrose, trehalose and D-sorbitol) and pectin methylesterase (PME). Two kinds of freezing methods have also been studied: blast freezing (BF) and immersion freezing (IF) (immersion in 30% CaCl2 or 66% glycerol). The L*C*h° color values, drip loss and relative hardness of thawed strawberry were investigated. The results show that strawberries were vacuum infused with 1% calcium chloride solution and frozen by BF, drip loss was 1.43%, relative hardness was 10.1%, there were no significant differences between L* value and h° value of fresh strawberries and thawed strawberries (p＞0.05). Strawberries were vacuum infused with 1% D-sorbitol solution and frozen by BF, drip loss was 0.12%, relative hardness was 18.2%, there were no significant differences between L* value and h° value of fresh strawberries and thawed strawberries (p＞0.05). Strawberries were pretreat with PME + 1% calcium chloride and frozen by BF, drip loss was 0.70%, relative hardness was 10.5%, there were no significant differences between L* value and h° value of fresh strawberries and thawed strawberries (p＞0.05). Freezing of strawberries with the above pretreatment methods by IF (immersion in 30% CaCl2), drip loss were 0.16%, 0.13% and 0.15%, relative hardness were 15.7%, 20.7% and 21.5%, respectively. Freezing of strawberries with the above pretreatment methods by IF (immersion in 66% glycerol), drip loss were 1.00%, 1.30% and 0.40%, relative hardness were 10.2%, 87% and 10.4%, respectively. Compared with BF, freezing of strawberries by immersion in 30% CaCl2 with lower drip loss and higher relative hardness. Microstructural studies show that the pretreatment methods with BF or IF the cell structure is intact. The sensory evaluation results shown that pretreatment methods (vacuum infused with 1% calcium chloride solution, vacuum infused with 1% D-sorbitol solution and pretreatment with PME + 1% calcium chloride) of frozen strawberries after thawed, possessed the best qualities of appearance, aroma, texture, taste and overall acceptability than commercial product. The result of the above pretreatment methods of frozen strawberries after thawed the quality similar to fresh strawberry. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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