Study On Antimicrobial Control And Fat Reduction Of Yangzhou Steamed Buns With Bok Choy Fillings

Yangzhou steamed buns are popular with China and Southeast Asian countries for the delicious taste and healthy nutrition.However,due to the high moisture content and rich nutrients,Yangzhou steamed bun wrappers are prone to deterioration.In addition,due to the high fat content,the internal filling is prone to oil-water separation in the actual processing,which cannot guarantee the standardized production of steamed buns.For this reason,steamed buns with bok choy(Brassica chinensis L.)filling are chosen as the experimental object,mainly aimed at controlling microbials of the wrappers and reducing fat content of the bok choy filling.The main contents and results are as follows:(1)Clove oil,cinnamon oil and ?-polylysine hydrochloride were chosen by three evaluation indexes including inhibition zone diameter,minimum inhibitory concentration(MIC)and fractional inhibitory concentration index(FICI).The antimicrobial agents showed better inhibitory effects to three indicator microorganisms(Escherichia coli,Staphylococcus aureus and Aspergillus niger)and the combinations showed synergistic or additive effect.After orthogonal experiment optimization,composite antimicrobial agent formula was ensured as: 37.5 mg/kg ?-PL-HCl,81.25 mg/kg cinnamon oil and 200 mg/kg clove oil.During the emulsion preparation,GC-MS results showed that the processing had little effect on the active antimicrobial components such as eugenol and cinnamaldehyde.The effects of temperature,NaCl concentration and storage experiments on several prepared emulsions were determined and the result found that the emulsion S1T1 showed good emulsion stability.In addition,the composite antimicrobial emulsion maintained good antimicrobial activity after being processed under simulated processing conditions of steamed buns.Meanwhile,the partial antimicrobial mechanism of emulsion was that the emulsion destroyed the integrity of the membrane and increased the permeability of the microorganisms membrane,leading to the leakage of intracellular substances.(2)The composite antimicrobial emulsion S1T1 was applied to the steamed bun wrappers,and it was found that the sample group with the emulsion concentration of 0.3%,0.4% and 0.5% exceeded the detection limit of the total number of colonies(5 log CFU/g)on 9 d,11 d and 13 d,respectively.Meanwhile,the detection limit of the total number of molds(150 CFU/g)was exceeded on 11 d,13 d and 17 d,respectively.Based on electronic nose principal component analysis and sensory evaluation,it was found that the concentration of 0.3% and 0.4% emulsion can achieve effective antimicrobial control without sacrificing the original flavor of the steamed bun wrappers.In addition,the addition of emulsion had no significant effect on the moisture content,hardness and color parameters of wrappers.Therefore,the composite antimicrobial emulsion can be expected to provide theoretical support and novel idea for controlling the microorganisms of steamed pastry and prolonging the storage time.(3)In the fat reduction study of bok choy filling,pre-emulsified soybean oil was prepared by ultrasonic emulsification method as a fat replacer for the filling.Pre-emulsified soybean oil consisted of soybean oil(30%),whey protein(2%),composite gum(0.2%,xanthan gum: guar gum=4:6)and pregelatinized starch(0.5%).Ultrasonic emulsification conditions were ultrasonic power of 480 W and treat time of 15 min.The average particle size and polydispersity index of the pre-emulsified soybean oil prepared by ultrasonic emulsification is 224.0±12.1 nm and 0.182±0.009,respectively.The pre-emulsified soybean oil was stable to sugar concentration and NaCl concentration at a given condition.(4)Applying pre-emulsified oil as a fat replacer to the bok choy filling,it was found that the replacement ratio of 33.3% and 66.7% soybean oil before and after steaming treatment had non-significant effect on the water and oil holding capacity and total color difference of the filling.Low-field NMR results proved that oil-water separation occurred in fillings with the replacement ratio of 100% soybean oil.At the same time,the replacement ratio of 33.3% and 66.7% reduced the hardness of the filling and maintained the similar flavor close to the control sample,and showed satisfactory overall acceptability.Therefore,pre-emulsified soybean oil could have a good application prospect as a fat replacer for reducing fat in green leafy-vegetable fillings.