阅读说明：本技术 一种液态脱脂乳及其制备方法 (Liquid skim milk and preparation method thereof ) 是由 张晓梅 艾娜丝 孙宝国 于 2019-10-22 设计创作，主要内容包括：本发明公开了一种液态脱脂乳及其制备方法,其步骤包括：1)将脂肪酶、醇类物质加入全脂乳中,进行酶解反应,得到酶解牛乳脂肪香基；2)取适量步骤1)中的酶解牛乳脂肪香基,离心分离得上层脂状物；3)将步骤2)中的上层脂状物加入脱脂乳中,经搅拌或均质,得到本发明的液态脱脂乳。本发明的液态脱脂乳及其制备方法选择全脂乳作为酶解底物,进行了全脂乳相关代表性成分的保存、富集并转移至脱脂乳中,使获得的脱脂乳产品在满足脱脂的条件下,同时具有良好的风味感官品质与结构状态品质。(The invention discloses a liquid skim milk and a preparation method thereof, and the method comprises the following steps: 1) adding lipase and alcohol substances into whole milk, and performing enzymolysis reaction to obtain enzymolysis milk fat essence; 2) taking a proper amount of the enzymolysis cow milk fat flavor base in the step 1), and performing centrifugal separation to obtain an upper-layer grease-like substance; 3) adding the upper-layer lipid substance in the step 2) into the skim milk, and stirring or homogenizing to obtain the liquid skim milk. The liquid skim milk and the preparation method thereof select the whole milk as an enzymolysis substrate, store, enrich and transfer the related representative components of the whole milk into the skim milk, so that the obtained skim milk product has good flavor sensory quality and structural state quality under the condition of meeting the condition of degreasing.)

1. A preparation method of liquid skim milk is characterized in that: the method comprises the following operation steps:

(1) adding lipase and alcohol substances into the whole cow milk at the temperature of 35-70 ℃ for enzymolysis reaction to obtain the enzymolysis cow milk fat essence; preferably, the reaction time is 30-300 min, and after the enzymolysis is finished, enzyme is deactivated and cooled;

the lipase is sn-1,3 site specific lipase; preferably, in the full-cream milk enzymolysis reaction system, the addition amount of lipase is 1-20U/mL of full-cream milk;

preferably, the alcohol substances are selected from alcohol substances allowed to be used in milk and dairy products in GB2760-2014, further selected from ethanol, propanol, propylene glycol, butanol, n-pentanol and n-hexanol, and optimally selected from one or two of ethanol and propylene glycol; preferably, in the full-cream milk enzymolysis reaction system, the addition amount of the alcohol substance is 0.5-5.0 mu L/mL of full-cream milk;

(2) centrifuging the enzymolysis milk fat aroma obtained in the step (1) for 5-25 min at 3000-15000 r/min at 5-25 ℃; preferably, the conditions are 10-20 ℃ and 5000-10000 r/min centrifugation for 10-20 min;

(3) and (3) separating the upper-layer grease-like substance of the fat base of the enzymolysis milk in the step (2) and adding the upper-layer grease-like substance into skim milk to obtain the liquid skim milk.

2. The method for preparing liquid skim milk according to claim 1, wherein in step (1), the whole milk is pasteurized whole milk or pasteurized raw milk, and the protein content is not less than 2.9%, and the fat content is not less than 3.1%.

3. The method for preparing the liquid skim milk according to claim 1, wherein the enzymolysis in step (1) is carried out at 35-65 ℃ for 120-300 min; preferably, the enzymolysis condition is that the temperature is 50-60 ℃ and the time is 150-200 min.

4. The method for preparing liquid skim milk according to any of claims 1 to 3, wherein the lipase in step (1) is immobilized or free lipase, specifically, the lipase is one or more of animal, plant, microorganism such as bacteria, actinomycetes, yeast and fungus sources, and the addition amount is 2 to 15U/mL of whole milk; preferably, the lipase is Palatase 20000L, and the addition amount is 5-15U/mL of full-fat milk, or the lipase is Lipozyme TLIM, and the addition amount is 2-10U/mL of full-fat milk.

5. The method for preparing liquid skim milk according to any of claims 1 to 3, wherein the alcohol in step (1) is a mixture of ethanol and propylene glycol, and the amount of the alcohol is 1 to 3 μ L/mL of whole milk, and the addition ratio is V_{Propylene glycol}:V_Ethanol= 1 to 6, (1 to 6) is optionally V_{Propylene glycol}:V_Ethanol= (2-5): (1-4), preferably adding ratio V_{Propylene glycol}:V_Ethanol= (2-4): (1-3), more preferably (2-3): 2-3); preferably, the alcohol substance is a mixture of ethanol and propylene glycol, and the addition amount of the alcohol substance is 1.2-2.0 mu L/mL of whole milk.

6. The method for preparing liquid skim milk according to any of claims 1 to 3, wherein in the step (1), the enzyme deactivation method is performed by selecting a heating method after the completion of the enzymatic hydrolysis, and the enzyme deactivation aims to deactivate lipase and terminate various types of enzymatic reactions, and preferably the enzyme deactivation conditions are 75 to 85 ℃ for 5 to 15 min; further, the cooling can be performed in an environment of 0-20 ℃ and the temperature is reduced to room temperature.

7. The method for preparing liquid skim milk according to any of claims 1 to 3, wherein the step (2) is to centrifuge the milk fat flavor of the enzymolysis milk obtained in step (1) for 5 to 25min at 3000 to 15000r/min at 5 to 25 ℃; the preferable conditions are 10-20 ℃ and 5000-12000 r/min centrifugation for 10-20 min; more preferably, the conditions are 10-15 ℃ and 8000-12000 r/min centrifugation for 10-15 min.

8. The method for producing liquid skim milk according to any of claims 1 to 3, wherein the skim milk in step (3) is pasteurized skim milk or non-sterilized skim milk, and the fat is less than 0.1%; the amount of the lipid material in the upper layer is 2 to 25g, preferably 5 to 15g, per 100mL of skim milk.

9. The method for preparing liquid skim milk according to any of claims 1 to 3, wherein the stirring conditions in step (3) are 5000 to 20000r/min, 1 to 5min, or the homogenization conditions are a primary pressure of 150 to 250bar and a secondary pressure of 50 to 100 bar; preferably, the stirring condition is 5000-7000 r/min and 1-2 min, or the homogenizing condition is 150-200 bar of primary pressure and 50-80 bar of secondary pressure.

10. The method for preparing liquid skim milk according to any of claims 1 to 3, wherein the sterilization conditions of the liquid skim milk of step (3) are pasteurization, preferably the sterilization conditions are 62 to 65 ℃, 15 to 30min, 72 to 75 ℃, 15 to 20s, 82 to 85 ℃, and 10 to 20 s; more preferably, the sterilization conditions are 72 ℃ for 15 s.

Technical Field

The invention belongs to the field of dairy product processing. In particular to liquid skim milk for improving flavor sensory quality by an enzymolysis technology and a preparation method thereof.

Background

With the popularization of the current healthy diet and the reasonable collocation life concept, the selection of consumers for food tends to lower the fat and the functionalization more and more. This trend towards changing consumer options also affects the dairy field, including the liquid milk market. At present, full-fat milk and skim milk are common main products in the liquid milk market. Wherein, the flavor and the mouthfeel of the whole milk are good, but the fat content of the whole milk is considered to be too high by consumers; meanwhile, although the fat content of the skim milk is low, the skim milk has the defect of insufficient milk flavor and taste. Therefore, the research and development of related milk products with low fat content and good milk flavor have wide market prospect.

Among the various milk ingredients, milk fat contributes most to the flavor quality of dairy products. In non-skimmed dairy products, the milk fat acts to solubilize the flavor and provide flavor precursors, providing flavor qualities to the dairy product. In the dairy industry, lipases are commonly used in the production process of dairy products with the aim of generating good flavour substances that have a positive effect on the dairy flavour. Under the action of endogenous or exogenous lipase and heat treatment processing technologies such as sterilization and the like, fatty acid in milk fat triglyceride can be released freely, and the milk fat triglyceride and other components in a milk system are subjected to different types and different degrees of physicochemical reactions, so that a series of various volatile flavor substances are generated, and the flavor quality of the milk product is improved.

In the research method for improving the milk flavor, the technical scheme of the commonly used enzymolysis milk fat is as follows: selecting proper lipase to carry out enzymolysis on milk fat products with high fat content such as anhydrous milk fat or butter and the like, and trying to achieve the purpose of improving the milk flavor by utilizing fatty acid volatile flavor substances released by the enzymolysis of the milk fat under an optimized enzymolysis condition. The flavoring method for enzymatic hydrolysis of anhydrous milk fat has some obvious advantages, firstly, because the content of the milk fat of the anhydrous milk fat and the butter is very high, and usually exceeds 90%, the method provides the most complete enzymatic hydrolysis substrate for lipase hydrolysis, and secondly, under the condition of the substrate with high milk fat content, the content of the generated fatty acid volatile flavor substances is very considerable. However, the method for enzymolysis of anhydrous milk fat or butter may not be suitable for increasing the flavor components of natural cow milk and improving the flavor quality of natural cow milk of liquid cow milk, and the reasons are mainly as follows: (1) because the fat content of the anhydrous milk fat or butter is very high, the anhydrous milk fat or butter must be melted by high-temperature heating and other methods to be fully contacted and reacted with lipase, and different solvents are often needed, which inevitably causes irreversible adverse heat-sensitive reaction and solvent residue in a reaction system, and if the anhydrous milk fat or butter is applied to liquid milk products, the natural degree of the milk flavor of the products is often reduced; (2) because the fat content concentration of the reaction system is extremely high, the type of reaction for enzymatic flavor enhancement is often related to high-degree oxidation reaction of milk fat, and besides releasing a large amount of fatty acid substances, methyl ketone substances and aldehyde substances with higher content ratio are generally generated. In the volatile flavor substance types with the flavor of natural milk, except the short carbon chain fatty acid substances with higher content, the content of the ester substances is also higher, meanwhile, the general content proportion of the methyl ketone substances is moderate, and the content proportion of the aldehyde substances is very low. In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention provides liquid skim milk and a preparation method thereof, and the prepared liquid skim milk has better milk flavor and tissue state.

The present application is based on the discovery and recognition by the inventors of the following facts and problems:

based on the prior art, analysis shows that the method for enzymolyzing the anhydrous milk fat has a limited effect on increasing the flavor of the natural cow milk. If Pasteurized Whole Milk (PWM) is directly selected as the substrate for lipase enzymolysis, the total volatile flavor substances may not be produced in a content comparable to that of the hydrolyzed anhydrous cream, but the PWM itself has a better composition of the volatile flavor substances of natural milk than other milk fat products, so-called "homology of taste and food". Furthermore, according to the literature report and experimental results, it is found that since PWM is mainly a milk system in an aqueous environment, most of the natural milk volatile flavors are small molecular compounds with amphiphilic properties, and milk fat is more prone to be retained in a non-polar environment. PWM is colloidal solution containing more than 90% of water, wherein the main flavor substances are medium-short carbon chain fatty acid, and esters and ketones with simple structure. In the anhydrous milk fat, water is hardly contained, and the main flavor products after enzymolysis are ketones, lactones, aldehydes, heterocycles and the like, and then fatty acids, esters and the like; in PWM, main flavor products after enzymolysis are fatty acids, esters, ketones and other substances, and the components of the flavor products are consistent with those of PWM. Therefore, the PWM system with high water content can promote the dissolution of the volatile flavor substances with amphiphilic micromolecules, so that the balance direction of the reversible reaction of the milk fat enzymolysis is moved towards the enzymolysis direction, more volatile flavor substances with natural milk flavor components are generated, the milk fat enzymolysis in the PWM system is more thorough, and the target accuracy degree and the reaction efficiency of the reaction of the milk fat enzymolysis by the lipase are improved.

In the aspect of enzymolysis, the inventor imagines that the liquid skim milk has good flavor quality and is close to PWM, and the enzymolysis method is used for enzymolysis of the milk fat to release more medium-short carbon chain fatty acids and corresponding ester and ketone substances with simple structures, so that the good flavor substances with PWM characteristics are enriched. In order to achieve the purpose, the inventor adds alcohol substances into an enzymolysis system based on the following principles: under the sn-1,3 site specific enzymolysis effect, short carbon chain fatty acid in triglyceride release in milk fat is a reversible reaction, and an alcohol substance is added to generate an ester substance with the released fatty acid to a certain extent, so that the reaction moves towards the direction of releasing the fatty acid, more fatty acid is released, and the milk fat is more thoroughly enzymolyzed; further, the addition of ethanol produces fatty acid ethyl esters with fatty acids (which have a sweet and fragrant flavor). The milk fat can improve the milk flavor at low concentration, and can bring rancid flavor at high concentration, so that the possibility of rancid flavor is reduced by adding fatty acid ester substances generated by alcohol substances while the milk fat is expected to be subjected to enzymolysis to release short-carbon-chain fat at high degree. Further, in addition to the reversible reactions of enzymatic hydrolysis to release fatty acids, there are also reversible reactions of transesterification of milk fat triglycerides themselves, and synthesis of new triglycerides. And by adding alcohols such as propylene glycol and the like, a part of triglyceride can be subjected to transesterification or the alcohols and the acids can be synthesized into new glycerides, so that the reaction can bring benefits to the structural property of the system, a certain amount of fat spheres can be ensured to exist in the system, and the fat spheres have larger particle size, so that the fat spheres have benefits for improving the mouthfeel consistency and the system stability.

The enzymolysis milk fat base which has complete enzymolysis reaction, abundant and good flavor substances and good system property is obtained through the enzymolysis series reaction, and the liquid skim milk prepared by using the base has the quality of better approaching to the flavor of natural milk and thicker mouthfeel under the condition of ensuring that the milk fat content is lower than 0.5 percent. The technical solution of the present invention is finally formed based on the above factors, reasons and reasons.

The invention firstly provides a preparation method of liquid skim milk, which comprises the following steps:

(1) carrying out enzymolysis reaction on the whole milk for 30-300 min by using lipase and alcohols under the condition of 35-70 ℃, and carrying out enzyme deactivation and cooling after the enzymolysis is finished to obtain the enzymolysis milk fat essence;

preferably, the enzymolysis condition is 35-65 ℃ for 120-300 min; more preferably, the enzymolysis condition is that the temperature is 50-60 ℃ and the time is 150-200 min.

The lipase comprises sn-1,3 site specificity, immobilized or free lipase (International Classification No. EC3.1.1.3), the addition amount of the lipase in a full-fat milk enzymolysis reaction system is 1-20U/mL of full-fat milk, and specifically, the lipase is one or more of animal, plant or microorganism (such as bacteria, actinomycetes, yeasts and fungi) sources. Preferably, two or one of non-immobilized enzyme Palatase 20000L and immobilized enzyme Lipozyme TLIM with higher enzyme activity in a full-fat milk system can be selected; preferably, the lipase is Palatase 20000L, and the addition amount is 5-15U/mL of full-fat milk, or the lipase is Lipozyme TLIM, and the addition amount is 2-10U/mL of full-fat milk.

Wherein, alcohols in the enzymolysis reaction system can be selected from alcohols allowed to be used in milk and dairy products in GB2760-2014, and are further selected from ethanol, propanol, propylene glycol, butanol, n-pentanol, n-hexanol and the like. However, from the viewpoint of flavor and mouthfeel, the sensory scores of the esterification reaction involving ethanol and the esterification reaction involving propylene glycol are higher, and the sensory scores of propanol, butanol, n-pentanol and n-hexanol are lower. Furthermore, fatty acid ethyl ester substances generated by the esterification reaction in which ethanol participates generally have the flavor characteristics of fruity flavor and sweet flavor, and the flavor threshold is low, so that rancid flavor possibly caused by excessive fatty acid can be harmonized and weakened; the propylene glycol fatty acid ester substance generated by the esterification reaction of the propylene glycol has the advantages of stability, emulsification, no color and no taste, and has a positive effect of improving the thickening degree of the mouthfeel of the skim milk sample.

Therefore, preferably, the alcohol substance comprises ethanol or/and propylene glycol, the addition amount of the alcohol substance in the full-fat milk enzymolysis reaction system is 0.5-5.0 muL/mL of full-fat milk, preferably, the addition amount of the alcohol substance in the mixture of ethanol and propylene glycol is 1.0-3.0 muL/mL of full-fat milk, more preferably 1.2-2.0 muL/mL of full-fat milk, and preferably, the addition ratio is V_{Propylene glycol}:V_EthanolIs carried out in the ratio of (1-6) to (1-6), and is preferably added in the ratio of V_{Propylene glycol}:V_Ethanol(2-5) and (1-4), preferably V_{Propylene glycol}:V_Ethanol(2-4) and (1-3), more preferably (2-3) and (2-3).

After enzymolysis, a heating mode can be selected for enzyme deactivation, the enzyme deactivation aims to deactivate lipase and stop various types of enzymolysis reaction, and preferably, the enzyme deactivation condition is that the temperature is 75-85 ℃ and the time is 5-15 min. Furthermore, the cooling can be performed in an environment (such as an ice bucket) with the temperature of 0-20 ℃ and the temperature is reduced to room temperature.

(2) Centrifuging the enzymolysis milk fat aroma obtained in the step (1) for 5-25 min at 3000-15000 r/min at 5-25 ℃;

wherein, generally speaking, the temperature does not exceed room temperature during centrifugation, the rotating speed is not lower than 3000r/min, and the time is not lower than 5min, thereby ensuring the obvious separation of lipid phase and water phase.

Preferably, the conditions are 10-20 ℃ and 5000-12000 r/min centrifugation for 10-20 min. More preferably, the conditions are that the enzymolysis cow milk fat flavor base is centrifuged for 10-15 min at 8000-12000 r/min and 10-15 ℃ at 10-15 ℃.

(3) And (3) separating all the upper-layer lipid substances of the fat base of the enzymolysis milk in the step (2), adding the mixture into skim milk, stirring or homogenizing, sterilizing and cooling to obtain the liquid skim milk.

In a specific embodiment, the amount of the whole upper-layer grease-like substance of the fat-like base of the enzymolyzed cow milk should not exceed 25g/100mL of the skim milk and not be lower than 2g/100mL of the skim milk. Otherwise, the skim milk with a concentration of more than 25g/100mL may have a pungent bad flavor such as sour taste or bitter taste and a system instability such as uneven stratification; meanwhile, the skim milk with the concentration of less than 2g/100mL may not achieve the purpose of improving the flavor and taste of the skim milk. Therefore, the skim milk is preferably used in an amount of 2-25 g/100mL of the total upper fat of the milk fat flavor of the enzymolysis cow, and more preferably 5-15 g/100mL of the skim milk.

The stirring or homogenizing, sterilizing and cooling methods are conventional methods in the field, and aim to make the liquid skim milk system uniform and stable and have good sensory attributes.

In a preferred mode, the skim milk in the step (3) is pasteurized skim milk or non-sterilized skim milk, and the fat is less than 0.1%.

Further, the stirring condition in the step (3) is 5000-20000 r/min and 1-5 min, or the homogenizing condition is 150-250 bar of primary pressure and 50-100 bar of secondary pressure; preferably, the stirring condition is 5000-7000 r/min and 1-2 min, or the homogenizing condition is 150-200 bar of primary pressure and 50-80 bar of secondary pressure. In a more preferred embodiment, the sterilization condition of the liquid skim milk in the step (3) is pasteurization, preferably the temperature is 62-65 ℃ for 15-30 min, or 72-75 ℃ for 15-20 s, or 82-85 ℃ for 10-20 s; more preferably, the sterilization conditions are 72 ℃ for 15 s.

Further, the sterilized liquid skim milk is rapidly cooled in an environment of 0 to 4 ℃.

The invention also discloses the liquid skim milk prepared by the preparation method.

Compared with the prior art, the invention has the advantages that:

the method is simple to operate, the lipase is adopted to carry out enzymolysis on the whole milk to obtain the enzymolysis milk fat flavor base, and the upper layer fat is utilized to add the skim milk to obtain the liquid skim milk. Tests show that the liquid skim milk achieves a skim level (< 0.5%) in fat content and has good flavor sensory attributes and tissue state.

From the analysis result of the milk components, the obtained liquid skim milk meets the requirement that the fat content of the skim milk is not more than 0.5 percent. From the result of particle size distribution, RSMS (synthesized skim milk, i.e. the prepared liquid skim milk) and pasteurized milk of the same batch have substantially coincident particle size ranges, and the particle size of the liquid dairy product has a certain relationship with the thickness of the liquid skim milk due to the mouthfeel, which has a positive effect on improving the mouthfeel quality of the liquid skim milk.

In the aspect of flavor sense, the obtained liquid skim milk not only has volatile short-carbon-chain fatty acids which are common in the traditional enzymolysis method, but also has certain fatty acid esters, ketone substances, alkane substances, aldehyde substances and lactone substances. Wherein, the butyric acid, the caproic acid, the caprylic acid and the capric acid are common volatile flavor components in the fresh cow milk. From the sensory evaluation result, the liquid skim milk has better and full-bodied milk flavor and mouthfeel, wherein the milk flavor, milk mouthfeel and mouthfeel consistency are obviously improved compared with the common liquid skim milk.

Drawings

FIG. 1 shows the particle size distribution of RSMS and enzymolyzed fat bases and PWM and PSM of the same batch.

FIG. 2CLSM observes Nile red fluorescence labeling RSMS and enzymolysis fat perfume base and the same batch PWM, PSM milk fat globule microstructure. Wherein, A.RSMS, B.enzymolysis fat perfume base, C.PWM, D.PSM; a1, B1, C1, D1, Nile Red fluorescent Probe staining image; a2, B2, C2, D2, light microscopy images; a3, B3, C3, D3, overlapping the images.

FIG. 3 shows the back scattering light variation curves of RSMS and enzymolyzed fat bases and PWM and PSM of the same batch. Wherein, A.RSMS, B.enzymolysis fat perfume base, C.PWM, D.PSM.

FIG. 4 is a response diagram of the analysis results of the electronic nose of RSMS and PWM and PSM of the same batch. The system comprises a.RSMS, B.PWM and C.PSM.

Figure 5 score of various sensory evaluation indicators for liquid skim milk samples.

Detailed Description

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. The examples do not show the specific techniques or conditions, according to the technical or conditions described in the literature in the field, or according to the product specifications. The reagents or instruments used are conventional products available from regular distributors, not indicated by the manufacturer.