For simulating real pasteurization treatments using hot air,hot water,radio frequency and microwave heating,a unique experimental heating block system(HBS)was developed.The stability and uniformity of sample temperatures and heating rates in HBS were determined for studying the thermal resistance of food-borne pathogens.A computer simulation model was also developed to analyze the behavior of thermal process in HBS.The results showed that the required heating rates with various set-temperatures and holding times could be easily and precisely achieved in eight selected food materials.Thermocouple and thermal imaging data showed that the good sample heating uniformity in six cells of HBS was achieved.The real temperature-time histories obtained by radio frequency energy could be approximately done in HBS by setting a number of linear regression curves.The HBS can help in more precisely characterizing the heat resistance of pathogens in foods to further develop pasteurization processes.
Xiaoxi KouRui LiLixia HouTeng ChengXu ZhouShaojin Wang
Thermal treatments are commonly used for disinfesting chestnuts before storage.Color is a first and sensitive quality attribute of chestnuts after thermal treatments and storage.The purpose of this study was to investigate L*and b*values in chestnuts during thermal treatment at 50-70°C for periods varying from 0 to 160 min,and during storage at 3°C for 5 months using a computer vision system(CVS).Results showed that the L*and b*values decreased with increasing temperature,and heating or storage time.The first-order reaction model showed a better fit for the L*and b*values than zero-order reaction model with coefficients of determination(R2)ranging from 0.923 to 0.977 during the thermal treatment and storage.The activation energies of chestnuts were 287.19 and 347.48 kJ/mol during thermal treatments and 89.18 and 78.47 kJ/mol during storage for L*and b*values,respectively,suggesting that the yellowness(b*)was more sensitive to temperature changes than the lightness(L*).According to requirements of L*>50,a potential disinfestation treatment protocol could be developed for chestnuts at 52-62°C.
The sorption isotherms of full-fat(FPKF),partially defatted(PDPKF),and totally defatted(TDPKF)pistachio kernel flour were performed in the range of water activity(aw)from 0.113 to 0.859 at 15℃,25℃and 35℃,and the applicability of six mathematical models(Smith,Oswin,Henderson,GAB,Halsey and BET)in data prediction was evaluated.Sorption isotherms were typeⅡ,according to Brunauer’s classification.Equilibrium moisture content(EMC)increased with an increase in aw at constant temperatures.The sorption isotherms of all three flour samples exhibited hysteresis.Significant differences were found among equilibrium data of FPKF,PDPKF and TDPKF samples.TDPKF showed higher hygroscopic characteristics than PDPKF,and PDPKF showed higher hygroscopic characteristics than FPKF at any temperature and aw studied.It was found that the Smith model was the most satisfactory one for representation of the sorption data of full fat sample,but for defatted samples,Halsey was the best model.The average monolayer moisture content(MMC)calculated by GAB model were 2.443-3.781 g/100 g(d.b.),3.585-4.886 g/100 g(d.b.)and 5.093-6.918 g/100 g(d.b.)for FPKF,PDPKF and TDPKF,respectively.The isosteric sorption heat(Qst)calculated by means of Clausius-Clapeyron equation decreased with increasing moisture content.The Qst values were 44.76-74.67 kJ/mol,44.75-99.44 kJ/mol and 44.80-133.28 kJ/mol for FPKF,PDPKF and TDPKF,respectively,in the range of moisture content of 2%to 41%(d.b.)at 25℃.
