Study On Preparation Of Pork Flavor By Porcine Blood Enzymatic Hydrolysates Based On Thermal Reaction And Its Flavor Improvement

As people’s quality of life is improving, natural meat process flavor becomes popular. In our country, pork flavor is most familiar to us in daily life. However, most of the pork flavor on the market are formulated type, because of the indistinctive characteristic aroma. At present, meat and bones are used as basic materials for preparation of pork process flavor so that the cost is high. Porcine blood rich in protein is not utilized due to its dark red-brown color and bloody smell. In this study, porcine blood and lard were used as the basic material for preparing pork flavor. Enzymatic hydrolysis process and thermal reaction were used to weaken the bloody smell combined with lard oxidation. The aim was to obtain natural roasted pork flavor with the strongest meaty and characteristic aroma.The porcine blood corpuscle proteins were hydrolyzed by Papain and Flavourzyme sequentially. Based on the soluble solid content, hydrolyzing degree of enzymatic hydrolysates and sensory evaluation of thermal reaction products, the optimum enzymatic hydrolysis system was determined as follows: substrate concentration 10%(w/w), Papain dose 4000 U/g protein, enzymatic hydrolysis time 2 h, Flavourzyme dose 1440 U/g protein, enzymatic hydrolysis time 3 h.The enzymatic hydrolysates of porcine blood corpuscle proteins prepared under different enzymatic hydrolysis conditions were used to prepare pork flavor combined with oxidized lard and other materials. Solid-phase microextraction/gas chromatography–mass spectrometry(SPME/GC-MS) were used to characterize thermal reaction products. Partial least square regression(PLSR) was performed to analyze the correlation among relative molecular weight distribution of enzymatic hydrolysates, sensory attributes and volatile compounds of thermal reaction products afterwards. The results showed that 1-(2-furanyl)-ethanone, 1-octen-3-ol, octanoic acid, 3-hydroxy-2-methyl-4H-pyran-4-one, hexanoic acid, dihydro-2(3H)-furanone, octanal, 4-methyl-5-thiazoleethanol, 2-acetylthiazole, nonanal and 2-octenal were the key volatile compounds of pork process flavor. These compounds and peptides with the relative molecular weight in the range of 500 to 1000 had a significant and positive contribution to the aroma of pork process flavor.High-temperature thermal oxidation and mild enzymatic oxidation were used for oxidation of lard respectively. The oxidized lard and enzymatic hydrolysates of porcine blood corpuscle proteins participated in the preparation of pork flavor based on thermal reaction subsequently. The better high-temperature thermal oxidation system determined by orthogonal test was as follows: temperature 90℃, air flow 60 L/h, reaction time 60 min. Based on sensory evaluation, the better enzymatic hydrolysis system was obtained by single factor test. The condition was as follows: substrate concentration 60%(w/w), lipase amount 75 U/g lipid, enzymatic hydrolysis time 6 h. Sensory evaluation and GC-MS analysis showed that the thermal reaction product prepared by mild enzymatic oxidized lard was of better flavor and it was rich in volatile flavor compounds.Sensory evaluation and gas chromatography-olfactometry-mass spectrometry were used to assess bloody smell note and identify the characteristic flavor compounds of porcine blood corpuscle proteins enzymatic hydrolysates, thermal reaction products(without lard, with mild enzymatic oxidized lard, with high-temperature thermal oxidized lard), thermal reaction product with 10% flavor enhancing peptides added in and thermal reaction products prepared by different proportions of bones and blood enzymatic hydrolysates(1:0, 2:1, 1:1, 1:2). Results showed that the bloody smell mainly came from hexanal and methyl-urea. Thermal reaction could reduce the content of compounds with bloody smell significantly. With the flavor enhancing peptides added in, the bloody smell was covered by some volatile aroma compounds. Analysis of free amino acid composition and relative molecular weight distribution showed that free amino acids and peptides with the relative molecular weight below 500 could weaken the bloody smell. PLSR demonstrated that characteristic flavor compounds with burnt or roasted flavor such as 1-(4, 5-dihydro-2-thiazolyl)-ethanone, 1-hydroxy-2-propanone, furfural, 2, 5-dimethyl-pyrazine, 2-furfurylthiol, butyrolactone, 2-acetylthiazole and 2-pyrrolidinone showed significantly and negatively correlation to bloody smell. Hexanal and methyl-urea were positively but not significantly correlation to bloody smell. These compounds had a significant effect on covering the bloody smell. Therefore, the weakness of bloody smell was not totally attributed to the reduction of compounds with bloody smell. Bloody smell masking by compounds with burnt or roasted flavor was another important factor.