Abstract:

In this study, the evolution of several physico-chemical indexes (TPC content, conjugated diene, conjugated triene, and
peroxide value) and the low field nuclear magnetic resonance (LF-NMR) T2 relaxation characteristics (the relaxation time T21, T22,
T23, the corresponding peak area S21, S22, S23, and the single component relaxation time T2W) of lard were studied during the frying
process of potato chips at different loads. In each frying series, two frying loads were applied, namely 0.036 (high) and 0.015 kg of
potato/kg of lard (low) compared with blank control group without foodstuff. The correlation model between LF-NMR results and
physico-chemical indexes was established and experimentally verified. The results indicated that as the frying process prolonged,
the TPC content increased exponentially, conjugated diene and conjugated trienes increased linearly, and peroxide value increased
firstly and decreased later. A good binomial relationship was obtained between S21 or T2W and frying time. No obvious relationship
was found between frying time and S22, S23, T21, T22 or T23. With an increase in frying load, TPC content and K270 increased
significantly, and T2W decreased markedly. Regression analysis showed that TPC content, conjugated diene, conjugated triene
and peroxide value had excellent correlations with S21 and T2W. The models could be used to predict the changes in physicochemical
indexes by the LF-NMR characteristics of frying oil.

Key words: lard, frying, physico-chemical indexes, low field nuclear magnetic resonance (LF-NMR), relaxation characteristics