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Cheddar Cheese from Cow Milk with Elevated Conjugated Linoleic Acid Levels

Mian Anjum Murtaza*, Nuzhat Huma, Zafar Hayat, Mian Shamas Murtaza, Asif Meraj

Institute of Food Science and Nutrition, University of Sargodha, Sargodha, Pakistan

Abstract: The aim of the study was to evaluate the effect of feed management on conjugated linoleic acid (CLA) level in milk and subsequently on fatty acid profile of cheese. Twenty cows were divided into 2 groups, fed on grass silage and pasture feed with sunflower supplementation for 14 days. Milk samples were collected and analyzed for composition and fatty acid profile using gas chromatograph. Cheddar cheese was manufactured from both milk types and ripened for 120 days. During ripening, it was analyzed for composition and fatty acid quantification. The supplemented diet significantly increased the CLA content in milk. Similarly the cis-9, trans-11 CLA content in Cheddar cheese were more than twofold in case of supplemented diet as compared to grass silage. During ripening, CLA concentration remained stable. The sunflower supplementation showed no effect on cheese composition. Hence, supplemented pasture resulted in elevated CLA content in milk compared to grass silage.

Keywords: milk, fatty acids, cheddar cheese, conjugated linoleic acid

Received August 04, 2014; Revised August 10, 2014; Accepted August 14, 2014

Citation: Mian Anjum Murtaza, Nuzhat Huma, Zafar Hayat, Mian Shamas Murtaza, Asif Meraj, Cheddar Cheese from Cow Milk with Elevated Conjugated Linoleic Acid Levels. Journal of Food and Nutrition Research, 2 (8). 506-509. January 2014. doi:10.12691/jfnr-2-8-12

1. Introduction

Cheddar is a hard type of cheese having high nutritional value owing to the concentration of caseins, fat, minerals and vitamins [1,2]. It is a biochemically active product that experiences momentous changes during ripening[3].It undergoes a multifarious chain of microbial and enzymatic reactions responsible for the characteristic flavor and texture [4,5].

Milk composition is an imperative parameter that influences the quality of Cheddar cheese and affects the development of discrete flavor and texture properties all through manufacturing and ripening [6,7]. It is influenced by individuality, breed, species, and stage of lactation, health, nutritional status and diet management of producing animals [8,9]. Diet management plays a key role in modulating the milk composition particularly fatty acid profile of ruminant milk [10].

Milk fat is accountable for hypercholesterolemia since it comprises the cholesterol and saturated fatty acids [11]. The consumption of saturated fatty acids sources the elevation in low density lipoprotein. It is obvious that there is a positive correlation between the high cholesterol and the arteriosclerosis sickness [12].

A recent inclination of the food market is to offer products with lower or modified fat profile [13]. Milk fatty acid profile can be tailored by directly adding fatty acid supplements to milk and its products, by manipulating the genetic, or by providing particular diets to animals [14]. Directly adding supplements is the simplest technique to get desired level of fatty acids however; its shortcoming is odd flavors associated with sources [8,14].

Conjugated linoleic acid (CLA) refers to the set of positional and geometric isomers of linoleic acid having conjugated double bonds in the chain. Dairy products and meat from ruminants are the richest natural sources of CLA [15]. It is a natural component of milk fat. The hydrogenation of linoleic and linolenic acids by microbes is mainly responsible for its production in the rumen during the formation of stearic acid [16]. CLA shows positive impacts on human health like improved immunity, anticancer and antiatherogenic actions and lessening the body fat [17]. Its existence in human body is mostly coupled with ingested foods rich in CLA as compared to its endogenous synthesis [18]. Hence, CLA concentration should initially be elevated in rumen milk through diet management in order to naturally supplement the dairy products with CLA.

Keeping the above facts in view, the study was designed with the objective to assess the influence of feeding sunflower oil on CLA content in milk fat and its subsequent impact on fatty acid profile of Cheddar cheese during ripening.

2. Materials and Methods

2.1. Diet Management and Milk Collection

Twenty dairy cows of almost parallel calving dates and milk yield were fed full time on pasture for 96 days and had received no supplement. Then these were divided into 2 groups (10 cows in each group), one was fed on grass silage and typical concentrate (control) and other on pasture feed and supplement containing sunflower oil @ 100 g/kg (Suppl.) for next 14 days. Milk samples for analysis and cheese manufacturing were collected on 14th day from each cow. The milk was pooled and representative (for analysis) as well as bulk (for cheese) samples were taken in triplicate.

2.2. Milk Composition

Basic composition of milk was measured following the standard procedures given by AOAC [19]. Moisture content was determined by oven drying, protein by Kjeldahl method, fat content using Gerber method, pH was measured with a pH meter (inoLab WTW Series 720)after calibrating with fresh pH 4.0 and 7.0 standard buffers and lactose contents using Fehling solutions.

2.3. Milk Fatty Acid Analysis

Milk fat samples were obtained as described by Murphy et al [20]. These samples were methylated by acid-catalyzed methylation to make fatty acid methyl esters (FAME) following the protocol given by Stanton et al [21]. Fatty acids were quantified using a gas chromatograph (Varian, Harbor City, CA), having a flame-ionization detector. The data was analyzed using Varian software system 4.5. Fatty acids were identified with reference to retention times of standards (Sigma-Aldrich, St. Louis, MO) and quantified with regard to the internal standards. The results were calculated in g/100 g of total FAME.

2.4. Cheddar Cheese Manufacturing

Milk was standardized (fat to protein ratio 0.97:1.00) and used for Cheddar cheese manufacturing with mesophilic starter cultures and rennet (Chr. Hansen Ireland Ltd., Cork, Ireland) following the standard protocol described by Scott [22]. The samples were stored for ripening at 6-8°C for 120 days.

2.5. Cheese Composition

Fresh cheese was analyzed for moisture, protein, fat, salt and pH value following the protocols of AOAC [19]. Moisture content was determined by oven drying, protein by Kjeldahl method, fat content using Babcock method and salt content by Vol hard method. The pH of cheese slurry prepared by blending 20 g of grated and shredded cheese sample with 12 ml of water, was measured with a pH meter (inoLab WTW Series 720)after calibrating with fresh pH 4.0 and 7.0 standard buffers.

2.6. Cheese Fatty Acid Profile

Cheese was sampled for fatty acid profile at 0, 60 and 120 days of ripening. 15 g of grated cheese was mixed with 25 g freshly prepared of ammonium thiocyanate solution (30% wt/volume). Then it was placed at at 60°C for 60 minutes in water bath and centrifuged at 538 g for 20 min. The fat layer was separated and stored at 4°C. Methyl esters of fatty acid were prepared and quantified as described above [21].

2.7. Statistical Analysis

The results obtained for composition and fatty acid quantification of milk and cheese were analyzed statistically using SAS and procedures described by Steel et al [23].

3. Results and Discussion

3.1. Milk Composition

Compositional analysis of raw milk revealed that supplementation of sunflower significantly decreased the fat and subsequently increased the protein and lactose concentrations (Table 1). These findings are in accordance with the results reported by Kay et al [24].

Table 1. Composition of raw milk and cheese

3.2. Milk Fatty Acids

Table 2. Fatty acid profile of raw milk

Fatty acid profile of cow milk under trials is given in Table 2. There was a significant increase in proportion of linoleic acid content in milk from animals fed on supplemented diets. It might be owing to the high levels of linoleic acid in sunflower oil. Most of other fatty acids were also considerably influenced from supplemented diet. As a whole the significant decrease in the quantities of short chain fatty acids and increase in long chain fatty acids was observed. However, butyric acid and linolenic acid were the exceptions, which remained constant. The significant decrease in palmitic acid and increase in stearic acid concentrations were recorded in supplemented diet milk as compared to control (grass silage and concentrate). These variations in fatty acid concentrations are comparable to those reported by Murphy [25].

A highly significant increase in the quantities of C18:1 and C18:2 were found. These results undoubtedly reveal that sunflower supplemented diet effectively increased the concentration of CLA in cow milk within 2 weeks only. This shows the valuable impact of sunflower oil supplementation in diet to increase CLA contents as reported by Coakleyet al [16] and Kay et al [24].

3.3. Cheese Composition

As a result of elevated CLA level in milk, no significant variation in cheese composition was found compared with control treatment (Table 1).

3.4. Cheese Fatty Acid Profile

Fatty acid profile of Cheddar cheese during ripening of 120 days in summarized in Table 3. The variations in fatty acid concentrations in cheese owing to the use of supplemented diets and subsequent increase in CLA levels were comparable to those found in raw milk from which it was manufactured as were established by Dhimanet al [26]. Most of the fatty acids particularly the CLA concentrations remained stable during 120 days of ripening. Due to supplemented diet, vaccenic acid (C18:1 trans-11 vaccenic acid; TVA) concentration increased significantly in fresh cheese and sustained during whole ripening period. This fatty acid is also produced intermediary and takes part as substrate for bovine mammary desaturase enzyme [27].

Table 3. Fatty acid profile of Cheddar cheese during ripening

The concentration of cis 9, trans-11 CLA in cheese even at the end of 120 days ripening, was appreciable. This much quantity of CLA in combination with TVA, a few of which might be changed to CLA, can considerably contribute to the cis-9, trans-11 CLA level in human beings to have better health.

4. Conclusion

It was concluded that the concentration of CLA can be increased in milk and milk products through supplementation of pasture with oil containing high levels of linoleic acid. Moreover, the elevated CLA level in milk is transferred to the products resulting in increased health benefits.

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