The effects of blanching process applied before freezing storage on the quality properties of some vegetables

In this study, the physical, chemical and microbiological properties of unblanched and blanched before chilled -18 0C and stored at same temperature broccoli and sweet corn samples were examinated during the 12 and 9 months respectively.According to physical and chemical analysis results, Lightness (L*) value of all the broccoli samples florets and stems did not change significantly during the storage. Significant changes in a* and b* values of the all samples except unblanched broccoli florets were not also observed during the storage. Likewise broccoli samples, it was not determinated the siginificant changes of Lightness (L*) and b* value of the corn samples whereas a decrease in a* values of corn samples was determinated. According to the penetration force measurements to observe textural changes of the broccoli and corn, the blanching step caused softness in the broccoli samples, on the contrary, the blanching step caused hardness in the corn samples. Although, it was observed that the softness of unblanced broccoli samples was more than the blanched broccoli samples during storage. It was observed that the storage time and the blanching step effected on the quantity of solid content of broccoli samples while total solid content of corn samples were effected only by blanching step. Protein and ash contents of all the broccoli and corn samples have not changed significantly during the storage.Due to the blanching step, losses of Vitamin C content in both broccoli and corn samples was occured as expected, however it was observed that the losses of vitamin C-content of the unblanched broccoli and corn samples were more than the blanched samples. Peroxidase enzyme assay showed that the peroxidase activity has increased rapidly in unlablanched corn and broccoli samples during the storage, while less enzyme regeneration occured in blanced samples. It was found that the changes of lipoxigenase enzyme activity of corn samples was similar with the changes of peroxidase activity of broccoli samples.According to the results of microbiological analysis; Aerobic psychrotrophic bacteria was not observed in the blanced broccoli and corn samples depend on blanching effects. A rapid decrease of aerobic psychrotrophic bacteria counts was observed in the unblanched broccoli and corn samples in the first 7 days of storage. Moreover, aerobic psychrotrophic bacteria counts in the unblanched samples decreased gradually after 60th day of storage. On the other side, it was observed that the unblanched samples had higher mould-yeast count than the blanched samples during the storage and mould-yeast count decreased significantly in both broccoli samples in 90th day of storage. It did not found mould-yeast in the blanched corn samples while there was a significant decrease was observed in unblanched corn samples in terms of mould-yeast counts.According to the results of consumer test; it was not observed a significant difference between fresh corn, frozen corn with blanched and frozen raw corn in terms of colour and flavor properties on the contrary, there was a significant difference was observed in texture properties of corn samples.The enzymes in structure of product were made enough inactivity by the blanching process prevents negative changes during the frozen storage. Although, in the blanching process, the colour of product is been getting well and during the storage the colour of product is provided better protection.As a result, it is observed that the blanching before chilling is a necessary step for frozen storage of the broccoli and corn samples, blanched broccoli and corn samples provide its quality better.