Effects Of Moisture And Pore On The Oil Absorption Behavior Of Potato Chips

In recent years, fried food, represented by French fries and fried potato chips, is widely popular with consumers both at home and abroad. At present, the oil content of fried food is higher and the pathway and mechanism of oil absorption are not yet clear. Additionally, the measures of dropping oil content like pre-drying are lack of theoretical guidance and the researches on factors affecting oil absorption like material moisture and structure are defective. Therefore, the factors affecting oil absorption and how the oil enters the fried sample during the frying process must be discussed deeply. So restructured potato chips and actual potato chips were used as materials and the effects of material composition, material moisture content, frying conditions and initial pore diameter on oil absorption were studied in this paper.Firstly, in order to study the effect of material composition on the oil absorption, the restructured potato chips mixed with different proportions of potato starch, wheat gluten or soy protein isolated and water were used as materials. Different oil fractions were determined by staining method. It was found that the total oil(TO) content and structural oil(STO) content decreased as the protein concentration increased. TO contents of wheat gluten restructured system were less than soy protein isolate system, for 10.04%-16.69%.Secondly, the effect of material moisture content, including the moisture content during frying process and initial moisture content, on the oil absorption was investigated. It was observed that the oil contents of the pure starch restructured system and the actual potato chips increased as the moisture content during frying process decreased. Once and twice frying combined with confocal laser scanning microscopy(CLSM) was used to analyze the effect of initial moisture content on oil absorption. It was found that the contents of final TO and its oil fractions had no significant difference between once and twice fried samples(p>0.05). However, the twice-fried potato chips reached equilibrium than once-fried potato chips much more quickly(around sevenfold).Thirdly, the effect of frying conditions on oil absorption of the pure starch restructured system and the actual potato chips were studied. The results showed that oil content of restructured and actual systems both increased with the increase of frying time. The actual system was further studied. The low field nuclear magnetic resonance(LF-NMR) was used to observe oil distribution of fried chips in the frying process and mercury intrusion porosimeter was used to quantitatively analyze the properties of the pore of different samples. With the increase of frying time, more and more oil distributed in the interior of samples. And outer layer absorbed the highest oil content compared to other locations during the whole frying process. In the first 8 minutes, total pore volume and porosity of fried potato chips increased and bulk density decreased with frying time. In 8~12 min, the 3 parameters above remained constant at 1.63 cc·g-1, 0.42 g·cc-1, 68.7%. And it explained the effect of frying time on oil absorption from structure.Finally, the effect of initial pore diameter on the oil absorption was exploited with puncturing method. It was found that there was no significant difference in the oil contents among fried potato chips with initial pore diameter of 0, 0.1 and 0.2 mm(p>0.05). When the diameter was more than 0.3 mm, initial pore diameter had significant effect on TO and STO contents(p<0.05),both of which increased with the increasing of pore diameter. By comparing the variation of the contents of oil fractions, it was showed that STO fraction gave the greatest contribution to the increment of oil absorption. Additionally, the greater initial pore diameter of fried potato chips, the greater total pore volume.The research results showed that adding protein could reduce oil absorption. Initial moisture content had no significant effect on the final oil content(p>0.05) and the final oil content was more related to the space created by water evaporation instead of water itself. Moreover, oil content increased with the increasing of initial pore diameter. Taken together, this study laid the groundwork for introducing a pre-drying strategy to frying process in food industry and provided the scientific basis for establishing a regulatory mechanism of oil absorption during frying process.