Rapid detection of oil content and 3-dimensional reconstruction of microstructure of fried lotus root

Abstract: Recently consumption trends towards healthier and low fat products have played a significant impact on the snack industry. Lotus root slice is a kind of fried food. To improve and simplify the prediction model of oil content of fried lotus root slice, the synergy interval partial least squares (siPLS) and the net analyte signal (NAS) method were combined to search for the optimized informative spectral wavelengths about oil content from the high spectrum of fried lotus root slices, and then the spectral model was developed on the basis of oil content. Then the oil distribution in fried lotus root slices was non-destructively and rapidly measured by the step multiple linear regression (SMLR) models. Finally, the oil was stained by the Nile red. Confocal laser scanning microscopy (CLSM) is a new technology that can be used to observe the microstructure and oil distribution of fried lotus root slices after frying at atmosphere. A series of optical sectioning at different depths were obtained and then treated to make volumetric reconstructions. The results showed that the spectra were preprocessed by the SNV method and divided into 27 intervals, among which 4 subsets, i.e. No. 8, 10, 12 and 16 were selected by the siPLS. Then the NAS was used to characterize the net signals of oil content from the fried lotus root slice's spectra, which were used for regression variables of the NAS model. The NAS calibration model was obtained with the correlation coefficient of 0.819 in prediction set, and the root mean square error of 0.682 mg/g dry solid in prediction set. It proved that the siPLS-NAS could determine the optimal variables in high spectrum and improve the accuracy of model. In addition, the results showed that after frying, the cellular structures were well conserved in terms of shape and size. Oil showed to be mainly located on the surface of the crust formed. Oil remained in the enlarged intercellular space during the washing or the frying operation or in the damaged cells partially filled with starch. Cell detachment, because of starch swelling and dehydration, seemed to be the preferential connection between cell layers. The positive effect of frying at atmosphere on oil uptake reduction could be the restriction of these connections. Overall, this study has an important significance for decreasing oil uptake in terms of microstructure changes. Besides, it provides reliable data and effective means for the future study.