Studies on the quality of vacuum fried carrot chips and the oxidative stability of fried oil

• Main Authors: Shyu, Shyi-Liang, 徐錫樑
• Other Authors: Lucy Sun Hwang
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/30820117339695533701

博士 === 國立臺灣大學 === 食品科技研究所 === 86 === In part I , the effects of pretreatment and vacuum frying conditions on the quality of fried carrot chips were studied. The moisture and oil contents of fried carrot chips were apparently reduced when blanched carrot slices were pretreated by immersing in fructose solution and freezing prior to vacuum frying. More uniform porosity was observed on the cross section of carrot chips when examined by the scanning electron microscopy. During vacuum ying, the moisture content, water activity, color and breaking force of carrot chips decreased with increasing frying temperature and time while the oil content increased. The statistic analysis with the central composite rotatable design showed that the moisture content and breaking force of fried carrot chips were positively correlated with immersing sugar concentration, whereas the oil content and color quality of fried carrot chips were negatively correlated with immersing sugar concentration. Based on surface responses and contour plots, optimum conditions were: vacuum frying temperature of 95-105℃, vacuum frying time of 16-20min, and immersing fructose concentration of 30-40%. In part II , the purpose of this study was to evaluate the fring oil quality by different assessment methods during vacuum frying of carrot slices or vacuum heating (without frying). In six consecutive days, palm oil, lard and soybean oil were fried or heated under vacuum at 105 ℃ for 20 min. each hour in an 8- hour shift. Results showed that palm oil and lard possess greater thermal stability than soybean oil. As for the suitable assessment methods for vacuum fried oils, peroxide value, carbonyl value, total polar components and dielectric constant all showed good correlation between each other. In part III , the changes of chemical components of carrot slices during vacuum frying were investigated in this study. When carrot slices were blanched, frozen and fried under vacuum at 100 ℃ for 20 min to produce carrot chips, the retentions of α-carotene, β-carotene and ascorbic acid were 82%, 91% and 65%, respectively. The major acids found in carrot slices were malic, succinic and acetic acids. During vacuum frying, malic and succinic acid decreased while acetic acid increased. The contents of sugars and free amino acids decreased with increasing vacuum frying temperature (or frying time) , however, there was no significant changes in sugars and amino acids contents during frying at low temperature (below 90℃) . The fried carrot chips showed good retention of the chemical components because the frying process was carried out under vacuum and at low temperature(about 100℃). In part IV , the changes of the quality of various vacuum fried carrot chips which packed in PE pag during storage at room temperature for six months were studied. Sample A was prepared with frying at 100℃ for 20min . While sample B was prepared with frying at 125℃ for 4min, and commercial carrot chip was as sample C. Before storage, all samples had a lower water activi ty (below 0.25) . After storage for two months, all samples were still maintained a good quality. Nevertheless, for sample C, the water activity , moisture content and carbonyl value was apparently increased as the storage time increased. However , the color difference (△E) of sample B had the greatest increase among the three samples during storage. From the results of sensory evaluation, sample B had the lowest overall intensity among the three samples after storage for six months. Therefore, sample A had a better storage stability and higher quality than the other two samples.