Badania nad poprawą trwałości karotenoidów w liofilizowanej marchwi
AbstractCarrot contains high amounts of carotenoids (particularlyp-carotene), monosaccharides, minerals and dietary fibre, which makes it a valuable food that may be eaten raw or used in the processed state. The processing methods include freeze-drying. Freeze¬-dried carrot, that shows better sensory properties and reconstitution ability than the vegetable dried conventionally, could be used more frequently as a component of meal concentrates, especially instant products. Due to its porous structure, however, freeze-dried carrot is very unstable when stored: it quickly loses colour as a result of the decomposition of carotenoid pigments, also its taste and aroma change. Therefore, it is necessary to develop a method for maintaining the high nutritive and sensory quality of freeze-dried carrot for a longer storage time. The present study was thus designed to determine the conditions of the preliminary processing of the raw material and the parameters of freezing and drying that would ensure the maximum stability of the product in terms of colour and carotenoid content. The best stability of carotenoids was achieved for carrot blanched in a 0.4% extract of green tea or a solution of 0.2% L-ascorbic acid and 0.1% citric acid — such a product retained 30% of carotenoids after 6-month storage. When the blanching in the above solutions was followed by soaking in glycerol and/or sorbitol (2% of glycerol or 1% of glycerol and 1% of sorbitol), the retention of carotenoids increased to 50%. Equally good and desirable results were obtained by blanching in solutions containing L-ascorbic and citric acids or tea extracts with an addition of glycerol or glycerol and sorbitol, followed by chilling in air-blast instead of cold water. As a result of such a treatment, the final product maintained the characteristics of the freeze-dried product while being similar in stability to the conventionally dried one. The higher stability of carotenoids in freeze-dried carrot results also from a slower rate of freezing which causes ice crystals to enlarge in the frozen product. This leads to a greater accumulation of inter-crystalline matter that, in turn, ensures a lower porosity of the product. Freeze-dried carrot retains carotenoids and colour best when stored in the air with relative humidity ranging from ca. 23 to 40%. Lower humidity causes a faster loss of quality, whereas higher humidity, despite of the very good retention of colour and carotenoids, results in the excessive moisture, loss of crispness, changes in surface appearance, and sometimes even in gumminess of the product. Carrot stored in paper bags at room temperature and moderate relative humidity maintained a very good quality. Such properties of the dried material would make it possible to considerably reduce the costs of packing and storage in industrial conditions. Both the colour retention and carotenoid content of the stored freeze-dried carrot showed a high positive correlation with the dry matter content and carotenoid content of the raw material. This suggests that carrot intended for freeze-drying should have high contents of both carotenoids and dry matter. Such requirements are especially well fulfilled by late-maturing varieties which have already got recognition from the processing industry. The results of the sensory evaluation of colour were highly correlated with the carotenoid content of the dried product. The relationship was so close as to suggest that the sensory evaluation or instrumental measurement of colour may serve as an indicator of the carotenoid content of a dried product and the changes in its quality due to storage. The freeze-dried products had good rehydration properties. In general, they were not adversely affected by the pre-processing methods used in the study, except for the products with a dried surface (chilled in air-blast after blanching) whose time of rehydration was slightly longer than that for the other samples, including the control sample, while the total rehydration capacity did not differ from the other results. The findings from this study may provide a basis for the development of new products — convenient (ready-to-use) foods which will not only have attractive appearance and good storage stability but also be rich in nutritive components contained in carrot.
|Other language title versions||Studies on improvement in carotenoid stability in freezed-dried carrot|
|Publisher||Uniwersytet Rolniczy im. Hugona Kołłątaja w Krakowie, MNiSW |
|Publishing place (Publisher address)||Kraków|
|Book series /Journal (in case of Journal special issue)||Zeszyty Naukowe Uniwersytetu Rolniczego im. Hugona Kołłątaja w Krakowie. Rozprawy, ISSN 1899-3486, (0 pkt)|
|Publication size in sheets||5|
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