Effect Of Water Migration And The Structural Change Of Myofibril Proteins On Beef Quality During Sous-vide Cooking

Beef is the major category of meat consumed all of China,and considered as nutritious and delicious meat with high-protein and low-fat contents.Thermal treatments,including steaming,roasting,and frying,are often applied in meat products processing,However,high-temperature conditions are unavoidable when these traditional heating methods are used,resulting in textural deterioration,water holding capacity reduction,and nutrient loss in beef products.Therefore,it is of urgency to develop novel heating technology to maintain the original properties of beef products during processing.Sous-vide cooking has become one of the most representative,novel,and alternative mild-heating technologies,because of simple operation and low equipment dependence.Compared with traditional high-temperature heating methods,beef products are vacuum-packed and subsequently heated in a water bath within a precisely controlled low-temperature range during sous-vide cooking,which is ideal to maintain a series of sensory properties and avert beef product deterioration during thermal treatment.To date,most of the studies have focused on process optimization and their impacts on sensory properties of meat products during sous-vide cooking,yet how sous-vide cooking technology affects water migration and myofibril protein denaturation remains unclear.As a result,in the first section of this thesis,the impacts of different sous-vide cooking conditions on beef color differences,cooking loss rate,water holding capacity,and textural properties were characterized and further optimized.In the second section,physical appearance and other physicochemical property differences between raw beef and sous-vide cooked beef were analyzed,and the inner mechanisms were further elucidated from a perspective of water migration,using low-field nuclear magnetic resonance technology(LF-NMR).Finally,optical microscope and transmission electron microscopy(TEM)were carried out to show the microstructural and ultra-microstructural changes of beef muscles during sous-vide cooking,and the multi-level structure changes of myofibril protein,main structural proteins in beef,were also analyzed through electrophoresis,chromatography,spectroscopy.The main research results are listed as follows:(1)Process optimization of sous-vide cooking based on textural properties and water holding capacity in beef productsSous-vide cooking significantly affected the physicochemical properties of beef products and was closely related to heating parameters of temperature,time,and rate.According to the results of single-factor experiments,pH value,L^*value,and cooking loss rate of beef products increased,while a^*value decreased during sous-vide cooking.And the hardness and water holding capacity increased at the beginning of sous-vide cooking and then decreased.The results of response surface methodology demonstrated that the deterioration of beef muscles was minimized,and the water holding capacity remained at a high level during sous-vide cooking when the heating temperature was controlled between 60 and 65?.(2)Effects of sous-vide cooking on water migration in beef productsHeating at 65?within 90 minutes during sous-vide cooking changed the physicochemical properties of beef products,compared with those of raw beef,and these changes were significantly correlated to water migration properties,thus can be quantitatively conducted by principal component analysis(PCA).In detail,prolonged heating time accelerated the descent speed of the falling curve of water hydrogen proton lateral relaxation time,leading to the presence and the increased contents of free water(T₂₂),while diminishing the distribution of the phase of difficult-to-flow water(T₂₁),reducing the total water proton density and connecting strength between water and protein.As a result,the water holding capacity of beef decreased,the cooking loss rate increased,and the textural properties and surface morphology changed.(3)Effects of sous-vide cooking on(ultra)-microstructures and multi-level structures changes of myofibril proteins in beef musclesSous-vide cooking promoted a significant shrinkage on the beef muscle microstructures both horizontally and vertically,and an enlargement in the inter-fiber area during sous-vide cooking at65?within 90 minutes,while sous-vide cooking didn't change the ultra-microstructures compared with untreated beef.This can be attributed to the thermal denaturation of myofibrillar proteins,resulting in a decreased protein integrity and stability.During sous-vide cooking,the myofibrillar protein solubility decreased,the index of fiber fragmentation increased,the peptides of protein fractured,its secondary structure dissociated,and surface hydrophobicity increased.In this research,the effects of sous-vide cooking on the water holding capacity,textural,and other physicochemical properties in beef products were studied from the perspectives of water migration and myofibril protein denaturation,with the scope of providing raw experiment data support for sous-vide cooking-related studies in beef products.