Frying Oil Quality Control And Potato Chips Quality Analisis

Frying is one of the means commonly used in food processing. Frying oil was the heat transfer media, at the same time it gave the food a special texture and flavor. Fried food was very popular because of its special aroma and flavor, but its quality is closely related with the quality and safety of frying oil. This paper systematically researched the change of the physical and chemical indexes of frying oil with frying time in the course of frying, taking special frying oil as materials and potato chips as fried food, its quality control was also carried, and compared the change of indexes before and after the regulation. The rapid detection of near-infrared model of physical and chemical indexes of frying oil was established, the texture and microstructure changes of fried potato chips with frying time was also studied, all of these aimed to provide scientific basis on making better use of frying oil and fried food. The main results were as follows:(1)The change of physical and chemical indexes of the frying oil and the correlation between indexes were analyzed during frying process in this study. The results showed that the refractive index, color, acid value, carbonyl value and total polar material of frying oil were increasing with frying time; peroxide value changed irregularly with frying time; iodine value decreasing with frying time; there was no significant law in the change of specific gravity, viscosity and saponification value. There were very significant positive correlation among acid value, carbonyl value, total polar material, color and refractive index, and the correlation coefficients were greater than 0.9; total polar material of the frying oil can be predicted by the acid value and the color.(2)The quality control process using sodium silicate and activated bleaching clay was researched in this study, with frying oil and potato chips as raw materials. Through single and orthogonal experiments, the results showed the optimum conditions were: the total amount of sodium silicate and activated bleaching clay was 5%, the ratio of sodium silicate and activated bleaching clay was 1∶5, the reaction temperature was 84℃, and reaction time was 20min.We regulated the frying oil under this optimum condition, and compared color, acid value, carbonyl value, total polar material and peroxide value of the samples before and after the regulation. The results showed that the quality life of frying oil can be prolonged.(3)The quantitative analysis models of acid value, carbonyl value and total polar material of frying oil were established using near infrared spectroscopy. 80 near infrared spectroscopy data of frying oil samples were determinated, and the regression model were built using partial least squares. The results were: the coefficient of determination R~2 of the NIR model of carbonyl value, acid value and total polar material reached 99.04%, 96.17%, 84.56%, indicating that the established calibration models were of high quality. The external validation were carried using well-established calibration model, and the coefficient of determination Validation set were 97.81%, 98.76%, 89.84%, this can further validate the accuracy and stability of the model.Near infrared spectroscopy can effectively and quickly detect the changes of carbonyl value, acid value and total polar material of frying oil, providing the basis for the research of monitoring the frying oil in fast real-time.(4) In order to evaluate the quality change of fried potato chips, there was a systematic research about some physical indicators such as texture, moisture content, oil content and so on of potato chips with different frying time, as well as the shelf life prediction of potato chips in this study. The results showed that: the moisture content of potato chips were reducing, oil content were increasing, and the fragility had a comparatively large change with frying time; In the process of shelf life prediction, the acid value, peroxide value and carbonyl value of the oil from the potato chips were gradually increased, the shelf life prediction of potato chips was about 102d.(5) The microstructure of potato chips with different frying time was observed under scanning electron microscope and the microscope, the results showed that with frying time increasing, the potato slices were no longer smooth, and there were embossment and stomata formed. The oil absorbance occurred in the outside surface first, and the oil was slowly entering the potato from intercellular gap; with the gradual evaporation of water, the oil began to permeate into the cross-section. The starch granules and protein network structure in potato chips were gelatinized in high-temperature frying process.