| Lotus(Nelumbo nucifera Gaertn.)seeds contained rich carbohydrate,protein,fat and multiple kinds of bioactive substances.The Chinese have eat lotus seeds as food and medicine since ancient times,the lotus seeds is also considered to be a specific economic crop in China.However,the storage period of lotus seeds is shorter and the starch in it can easily retrograded during the processing.The processing of lotus seeds is currently too simplistic lack of highly processed products,which seriously restricts the development of lotus seed industry chain.Owing to delicious and good storage durability Puffed food is popular among the masses of young group,If the lotus seeds were processed into puffed food,they would have a broader market prospects.vacuum frying is a novel frying technology which can make the raw food dehydration under lower pressures.The vacuum fried lotus seeds are lower content lipid and the processing of it do little harm to nutritious value,color and taste.The main research content of the article is as follows:The optimization of the pretreatment of vacuum fried.The optimum pretreatment conditions were determined as a minimal oil content,maximum text and minimal change in color index.On the basis of single factor test and response surface method,The optimum pretreatment methods were found to be:blanching time 13 min,salt concentration 6.99%and freezing time 7 h.Under these optimal conditions,oil content,Fracturability and change in color index were found to be 26.3 1%、6.51 N and 9.9 respectivelyThe response surface methodology(RSM)was used to optimize vacuum frying procession of lotus seeds.A Central Composite Design(CCD)with three important factors of frying temperature(85～95℃),frying time(12-20 min)and vacuum degree(0.085～0.095 MPa),was used to study the response variables of fracturability(R1),color change(R2)and oil content(R3).As the result,frying temperature 95 ℃,frying time 12 min and vacuum degree 0.095 MPa were the optimum frying conditions.Under these conditions,fracturability,the change color and oil content reached 7.24 N,5.15 and 9.18%respectively.In addition,compared with Fried lotus seed at constant pressure,brittleness,color difference,oil content and sensory evaluation of the vacuum Fried lotus seed were significantly better.Fried lotus seed starch was highly gelatinization without obvious gap through electron microscopy observation,but the granule shape of starch and the large gap.inside lotus seeds could be clearly seen in fried lotus seed at constant pressure.The moisture loss and oil uptake kinetics of lotus seeds during vacuum frying were investigated at different initial moisture content(1.34,1.58 and 1.91 g/g db),temperatures(95 ℃,85 ℃ and 75 ℃)and vacuum degree(0.085 MPa,0.090 MPa and 0.095 MPa).Two empirical kinetic models were applied to fit the water loss and oil uptake during frying.The kinetic behaviour for oil uptake and water loss obey the model during frying.Therefore,the best fitting model to predict the vacuum frying kinetics was also proposed.The kinetic coefficients for moisture loss and oil uptake increased significantly(P<0.05)with these processing condition.The equation as follow:moisture dynamics model:M-Me =(M0-Me)exp(-Kmt)Me = 0.008134(T)0-01525(p)-0.4773(I)1.03776Km =0.010281(T)2.8857(P)4.1493(I)-0.60156Oil content dynamic model:F = Fe(1-exp(-Kft))Fe = 0.021582(T)0.97504(P)0.6292(I)1.04663Kf = 2.439883(T)0.90219(P)3.00289(I)-0.60176Furthermore,The different periods of time on the degree of peroxidation and acidity of the chips were studied.The first order kinetics of oil rancidity was applied to forecast the expiry period of vacuum fried lotus seeds and the peroxidation value and acid value data were collected respectively to fit with this kinetic models in different temperatures(10,20,30,40℃).As a result,the prediction model of peroxidation value was LnT=-0.0348 S + 7.2278,and the prediction model of acid value was lnT=-0.06545 + 9.582.The relative error of two models was less than ±10%. |
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