Effects Of Different Pretreatment Methods On Enzymatic Hydrolysis Of Aloididae Aloidi And Taste Characteristics Of Its Hydrolysates

Seafood condiment is recognized as new nutritional umami condiment following monosodium glutamate and chicken essence.It is produced by extraction,fermentation,enzymatic hydrolysis of seafood or the byproducts of seafood processing,among which enzymatic hydrolysis is one of the key methods of producing seafood condiment.However,some bottleneck problems,such as low efficiency,unpleasant flavor,and lack of umami flavor,restrict the development of seafood condiment industry.Many studies attempted to resolve those problems by focusing their studies on the screening of different protease and the optimization of hydrolysis parameters.Little information on improving enzymatic hydrolysis of seafood protein by pretreating the substrate are available.The substrate of protein is one of the key two factors affecting the enzymatic hydrolysis reactions,thus the enzymatic hydrolysis of protein should be influenced by the structural changes and denaturation of protein induced by different pretreatment.However,the effects of different pretreatment on enzymatic hydrolysis characteristics of seafood protein are still unclear.In this paper,a low economic value shellfish Aloididae aloidi was pretreated by heating,ultrasonic and oxidation processing before enzymatic hydrolysis,and the effects of different pretreatment on enzymatic hydrolysis characteristics of Aloididae aloidi and flavor properties of its hydrolysates were investigated,aimed to provide evidence for innovating the technique of enzymatic hydrolysis of seafood protein and the developing of the new seafood condiment.The main research contents and conclusions are as follows:1.The effects of different heating pretreatment conditions?heating temperature 50,70,90,100,121°C and time 5,10,15,20,25,30 min?before enzymatic hydrolysis on the enzymatic properties of the Aloididae aloidi and the flavor characteristics of the hydrolysates were investigated by determining the degree of hydrolysis,soluble peptides,flavor nucleotides,glutamic acid content and taste profile used electronic tongue,basing on the screen of protease species.The results showed when the mass ratio of neutral protease to flavor protease was 2:1,the hydrolysates showed good taste characteristics.With the increase of pretreatment temperature,the degree of hydrolysis,soluble peptides,taste nucleotides,glutamic acid content and umami taste first decreased and then increased,while the bitterness value showed a fluctuating trend that first decreased,then increased and then decreased.The prolongation of thermal pretreatment was not conducive to the hydrolysis of Aloididae aloidi protein and the accumulation of taste substances.To a certain extent,the heating pretreatment can improve the flavor and color of the Aloididae aloidi hydrolysates.The optimal pretreatment conditions are heating temperature 70?and heating time 10 min.2.The enzymatic hydrolysis system of Aloididae aloidi was pretreated by ultrasonic processing.The ultrasound power,ultrasound time,hydrolysis time,hydrolysis temperature,pH,liquid-solid ratio and enzyme addition amount were explored by single factor experiments.Plackett-Burman test and response surface optimization test were used to optimized the parameters.The results showed that showed that ultrasonic pretreatment had significant influence on the hydrolysis of shellfish,the hydrolysis degree rises first and fall later with the increasing of ultrasound power and pretreatment time.The optimum ultrasonic processing parameters were ultrasound power of 500W,ultrasound time of 20min and L/S ratio of 2:1,which resulted in DH of 41.33%.Then the combination of ultrasonic pretreatment and heating pretreatment?temperature70°C,time 10min?was used into enzymatic hydrolysis.We found that ultrasonic pretreatment could increase the content of free amino acids,5'-nucleotides,succinic acids,while the heating pretreatment could decrease the content of volatile compounds with grass and fishy flavor.The combination of different substrate pretreatment could improve the taste of hydrolysates and produced pleasant aroma,especially for the heating-ultrasonic pretreatment,which containing more volatile compounds such as ketones generated from Strecker degradation and ethyl butyrate.3.Aloididae aloidi was pretreated by different concentration of H₂O₂,basing on the double effects of protein denaturation and deodorization of oxidants.The results showed that the degree of hydrolysis could be increased in the samples pretreated by 5 mM and 20 mM H₂O₂.The content of free amino acids decreased with the increased concentration of H₂O₂,while the proportion of large molecular weight peptides increased.The moderate oxidation of protein of Aloididae aloidi is beneficial to the dissolution of 5'-nucleotide and succinic acid.The taste and aroma profiles of hydrolysates were obvious different from each other after pretreated by different concentration of H₂O₂.The hydrolysates of 5 mM,20 mM and 50 mM H₂O₂ pretreated samples contained more?E,E?-2,4-heptadienal and?E,E?-2,4-decadienal,while?E?2-hexenal and?E?-2-octenal could be detected in the hydrolysates of 70mM and 100 mM H₂O₂pretreated samples.The most diverse types of ketones were present in the hydrolysates of 70 mM H₂O₂ pretreated samples.The ester content of hydrolysates raised with the increased H₂O₂ concentrations.The PLSR method was used to established the correlation between MW,free amino acid,5'-nucleotide,organic acid and electronic tongue taste.The results indicated that more complex astringent,umami,bitter and aftertaste characteristics was mainly related to the bitter amino acids,succinic acid and the distribution of peptides with the molecular weight of lower than 200 Da,between 1000 and 2000 Da,or higher than 2000 Da,which was in the hydrolysates of 70 mM H₂O₂ pretreated samples.