Effect Of Isolated Lactic Acid Bacteria And Partial Substitution Of NaCl With KCl On Improving Quality Of Low-sodium Cheese

Cheese known as the "milk gold" has high nutritional value,and it is also considered as one of high sodium food sources.Excessive salt intake can increase blood pressure and reduce calcium absorption.Therefore,the amount of sodium salt added should be reduced in the cheese.Compared with normalsodium cheese,low-sodium cheese exist serious flavor defects,that is sour and bitter.The defects of low-sodium cheese(mainly flavor)affect the consumption of cheese,and some methods are used to minimize the flavor defects of low-salt cheese.A small amount of glutamic acid can produce umami.The interaction of umami and bitterness and sour can reduce bitter and sour.Glutamate decarboxylase negative starter(GAD-)should be screened as adjunct culture.With the aim of counteracting bitter of low-sodium cheese,dominant strains were isolated from raw milk and the maturity of 6 months of Cheddar cheese.Strains with excellent performance capability were selected preliminarily and were compounded,and the optimal combination was selected as adjunct culture.In order to obtain the optimum ratio of NaCl/KCl and achieve the reducing of bitter for low-sodium cheese when reducing salt,the optimal combination of adjunct culture and different ratios of Na Cl/KCl were used as the production of Cheddar cheese,and the quality of cheese was evaluated.First of all,dominant strains were separated by using MRS-CaCO3 medium and the contact enzyme test was used,and 21 Lactobacillus strains and 6 Lactococcus strains were preliminarily screened.Strains were screened by principal component analysis.These strains were determined for low growth temperature,acidifying capacity,autolytic activity,aminopeptidase activity and proteolytic activity.The results showed that strain C3 had less acid production,good proteolytic capacity and high autolytic activity;In addtion to less acid production,strain C4 had good proteolytic capacity and high autolytic performance;Strain C5 presented not only low acidifying activity,high aminopeptidase activity and high autolytic activity,but also high proteolytic capacity;Strain C7 exhitied medium autolytic activity and higher proteolytic capacity;Strain C8 displayed higher aminopeptidase activity;Strain C9 exhibited higher proteolytic capacity in addition to high autolytic activity;Strain C11 showed good performance in aminopeptidase activity and autolytic activity;Strain M5 displayed not only high aminopeptidase activity and high proteolytic capacity,but also higher autolytic activity;Strain Q1 had low acidifying and high autolytic performance;Strain Q6 exhibited not only less acid and high aminopeptidase activity,but also possessed good proteolytic capacity and autolytic activity.Strains C3,C4,C5,C7,C8,C9,C11,M5,Q1 and Q6 were evaluated for GABA content by high performance liquid chromatography(HPLC),and the results showed that strains C5,C8,C9 and Q6 contained < 5 ?mol/L GABA.Four selected strains were combinated by the determinated of acidifying capacity,autolytic activity,aminopeptidase activity and proteolytic activity,and C5,C8,Q6 were selected as adjunct culture of cheese by PCA.The combination of C5,C8,Q6 and different proportions of Na Cl and KCl(3:1,1:1,1:3)were used for cheese production,and then physical and chemical indicators and bitterness in different maturing cheese were determined.The results showed that the content of ash,fat,protein and potassium in the low-salt cheese was almost the same as the normal-salt cheese,but the proteolysis capacity increased and led to a large number of small molecular peptides and some free amino acids,and this increased the ratio of hydrophobic peptide to hydrophilic peptide,which in turn led to increase bitterness and softened cheese.Compared to low-sodium cheese,low-sodium cheese with adding adjunct culture possesed higher proteolysis capacity,more free amino acid and lower ratio of hydrophobic peptide and the hydrophilic peptide.Glutamate weakened the bitterness of the low-sodium,but bitterness was still high.The results showed that different ratios of NaCl/KCl had no effect on protein,fat,moisture,proteolysis and aminopeptidase activity in cheese,and the hardness and springness were not changed.By reversed-phase high performance liquid chromatography,it was found that glutamic acid content increased as the content of KCl increased.When KCl achieved a certain bitter threshold,it possesed bitter.The addition of 1NaCl/3KCl to cheese showed evident bitter.So the ratio of NaCl/KCl was higher than 1:1.The results showed that p H value of cheese with different ratio of NaCl/KCl and adding adjunct culture was lower than cheese with different ratio of NaCl/KCl,and proteolysis activity of cheese with different ratio of NaCl/KCl and adding adjunct culture was higher than cheese with different ratio of NaCl/KCl.At the same time,it possesed high aminopeptidase activity and lots of free amino acid.Moreover,it lower ratios of hydrophobic peptide/hydrophilic peptide and glutamic acid content increased.Cheese became soft and springness increased.Compared with normal-sodium cheese,cheese with different ratio of NaCl/KCl and adding adjunct culture showed higher aminopeptidase activity and lots of free amino acid.The content of glutamic acid was aslo higher and bitter value was lower.It had lower proteolysis activity and raatios of hydrophobic peptide/hydrophilic peptide than low-sodium cheese.But the content of glutamic acid increasedand bitterness of low-salt cheese was reduced.The results showed that the combination of the strains C5,C8 and Q6,Na Cl/KCl ratio of 1:1 were choosen,because of cheese with the addition of the starter and 1NaCl/1KCl cheese having better score.