| The Nemipterus virgatus are the second largest fish species for processing surimi products with large catch and their surimi has an excellent gel performance.During the rinsing stage of surimi production,a large amount of nutritious and valuable fish lipids are discarded for concentrating myofibrillar proteins and reducing lipid oxidation during storage,and then obtain the better quality frozen surimi,which severely influences the quality and flavor of surimi products.In order to improve the quality and flavor of surimi gels,exogenous oils/fats are usually added as texture modifiers,color enhancers and processing aids during the subsequent production of surimi products.Different types of fats/oils contain different fatty acid compositions and contents,which has different effects on the quality and nutritious values of surimi gels.And directly adding oils to the surimi will increase the oxidation of oil and have adverse effects on the water holding capacity and texture of the gel.Thus it is necessary to explore the effect of the amount and way of adding oil on the quality of surimi gels.Therefore,the objective of this study was to explore the types,addition methods and amounts of vegetable oils on the quality and flavor of the Nemipterus virgatus surimi gels,and to elucidate the interactions between external oils and protein molecules of surimi gels.1.2% peanut oil,soybean oil,corn oil,coconut oil,olive oil and safflower seed oil were added to compare the effects of vegetable oils on the gel quality of the Nemipterus virgatus surimi gels.The results showed that the addition of 6 kinds of vegetable oils could improve the whiteness and sensory properties of the Nemipterus virgatus surimi gels,but it had an adverse effect on the texture of the gels with the water holding capacity decreasing and the cooking loss rate increasing(P < 0.05).And the lipid oxidability and lipoxygenase activity of the gels also increased(P < 0.05).Comparative analysis showed that peanut oil and olive oil were rich in monounsaturated fatty acids such as oleic acid,which had poor emulsification effect with myofibrillar protein.And thus the oil droplets were easy to accumulate with the wide oil droplet diameter distribution range,and mainly distributed in0.10-0.25 ?m.Coconut oil was rich in medium-chain saturated fatty acids such as lauric acid,which was easy to solidify and agglomerate at low temperature.And the oil droplets with the diameter of 0.10-0.40 ?m were unevenly distributed in gel matrix.However,soybean oil,corn oil and safflower seed oil were rich in polyunsaturated fatty acids such as linoleic acid,which had a strong emulsification effect with protein.The oil droplets were evenly distributed in the gel with the small particles and small oil droplet diameter distribution range,and mainly distributed in the range of 0.05-0.15 ?m.And thus the gels exhibited a dense network with the small and uniform pore size,which effectively improved the quality of the gels(P < 0.05).Based on the analysis of gel quality,oxidation and nutritious characteristics,soybean oil and safflower oil are selected for further experiments to explore the effect of the adding way of oil on the quality of surimi gels.2.The effects of 2% soybean oil and 10% pre emulsified soybean oil(i.e.soybean oil emulsion pre-emulsified by whey protein isolate or sodium caseinate,containing 2%soybean oil)on the gel quality of the Nemipterus virgatus surimi gels were compared.The results showed that the whiteness of the Nemipterus virgatus surimi gels were improved by adding 2% soybean oil,while the texture properties were deteriorated,accompanied by decreased water holding capacity and increased cooking loss rate(P < 0.05).An uneven distribution of oil droplets with a diameter in the range of 0.10-0.175 ?m was observed in the gel matrix accompanied by obvious aggregation of oil droplets.And the gel with soybean oil exhibited a three-dimensional network with large cavities,and the oxidizability of lipids in it was significantly increased compared with the control without soybean oil(P< 0.05).However,after adding 10% pre-emulsified soybean oil,the whiteness,water-holding capacity and bound water content were significantly increased together with a decrease in the cooking loss rate(P < 0.05),whereas the texture and the oxidizability of lipids were not significantly changed(P > 0.05).Furthermore,the sensory properties of surimi gel were significantly improved.The pre-emulsified oil droplets with a diameter of less than 0.10 ?m were evenly distributed in the gel matrix,and the gel exhibited a three-dimensional network with small cavities and smooth surface.Therefore,pre-emulsified soybean oil with milk protein can effectively improve the gel properties and flavor of the Nemipterus virgatus surimi,which will be useful for the development of new surimi products.3.The effect of different pre-emulsified safflower seed oil on the quality and flavor of the Nemipterus virgatus surimi gel was explored the effect and mechanism.The results showed that the whiteness,water holding capacity and bound water content were significantly increased together with a decrease in the cooking loss rate(P < 0.05)as the contents of safflower seed oil increased up to 2%.And the oil droplets with an average diameter of less than 0.075 ?m was evenly distributed in the gel matrix,and the gel exhibited a three-dimensional network with small cavities and smooth surface.However,when the safflower seed oil contents exceeded 3%,the texture of gels were deteriorated with the increase of cooking loss rate and the decrease of water holding capacity(P < 0.05).In addition,volatile analysis stated that the control and Nemipterus virgatus surimi gels with 1%,2%,3%,4% and 5% safflower seed oil contained 48,56,57,62,60 and 61 volatile compounds,respectively.Characteristic volatile components included aldehydes,alcohols,hydrocarbons,and ketones,mainly resulting from oxidation and decomposition of oils by the activation of lipoxygenase,which synergistically contributed to a unique flavor of gels.The low contents pre-emulsified safflower seed oil could produce fine and uniform oil droplets and then played a role as filler particles to occupy the void spaces in gels,which resulted in the gels exhibiting a dense three-dimensional network structure.Consequently,the low contents of pre-emulsified safflower seed oil can be used as exogenous additives for enhancing the gel properties and giving a unique flavor of the Nemipterus virgatus surimi products,which also coincides with the development trend of low-fat and high-protein diet. |
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