Evaluation of Correlation between Acid Degree Value and Peroxide Value in Lipolysis of Control and Iron Fortified Caprine Milk Cheeses during 4 Months Storage

Elevation of acid degree values (ADV) and peroxide value (POV) indicates deterioration of nutritional and sensory qualities of dairy products during storage. Iron fortification in bovine milk cheeses in relation to lipolytic parameters and their correlations have been studied, while no such studies have been reported on caprine milk cheeses. The objectives of this study were to evaluate levels of ADV and POV of iron fortified [regular ferrous sulfate (RFS) and large microencapsulated ferrous sulfate (LMFS)] goat milk Cheddar cheeses compared to those of non-fortified control cheese (CC) and their correlations. Three batches of 3 types (CC, RFS and LMFS added) of goat milk cheeses were manufactured and stored at two temperatures (4 ̊C and −18 ̊C) for 0, 2 and 4 months. Iron was supplemented to RFS and LMFS cheeses by 8.23 g and 9.03 g per 9 kg, respectively. ADV and POV were determined using standard methods of examining dairy products (Richardson, 1985) and AOCS (1975) procedures. Results showed that ADV values for CC, RFS and LMFS cheeses for 0 and 4 month storage at 4 ̊C were: 0.67, 0.73, 0.64; 1.24, 1.78, 1.58, respectively, indicating significant (P < 0.05) elevations occurred in ADV for all three cheeses during 4 months storage. The cheese samples at 4 months storage showed significantly (P < 0.05) higher peroxide values compared to 0 and 2 month stored ones. The samples stored at refrigeration temperature (4 ̊C) revealed slightly more lipid oxidation than those stored at frozen temperature (−18 ̊C). Significant (P < 0.05) elevations in POV for all goat cheeses stored for 4 months and slight increases in POV at higher temperature implies that the longer time and higher temperature storage can elevate the rate of lipid oxidation in goat milk Cheddar cheeses. How to cite this paper: Siddique, A. and Park, Y.W. (2019) Evaluation of Correlation between Acid Degree Value and Peroxide Value in Lipolysis of Control and Iron Fortified Caprine Milk Cheeses during 4 Months Storage. Open Journal of Animal Sciences, 9, 1-11. https://doi.org/10.4236/ojas.2019.91001 Received: October 29, 2018 Accepted: December 17, 2018 Published: December 20, 2018 Copyright © 2019 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access DOI: 10.4236/ojas.2019.91001 Dec. 20, 2018 1 Open Journal of Animal Sciences A. Siddique, Y. W. Park Correlations (r) between ADV and POV for the pooled data of three types of the caprine cheeses across storage periods were significant (P < 0.01), while r values of CC cheeses alone were negative. It was concluded that significant correlations exist between extents of lipolysis and lipid oxidation in the caprine milk Cheddar cheeses during 4 months storage.


Introduction
Quality of dairy products has been evaluated by various analytical methods. Lipolysis is the hydrolysis of lipids catalyzed by lipase enzymes, which has been a major dairy industry problem due to its implication of rancid flavor defect in milk, cheese and other dairy products [1]. Flavor deterioration resulted from lipolysis of dairy products has caused serious industry problems in storage stability and consumer acceptability [2] [3]. Lipolysis of goat milk cheeses has been estimated by acid degree value (ADV), acid value, and free fatty acid concentration, while lipid oxidation of dairy goat products can be determined by peroxide value, thiobarbuturic acid value (TBA) [1] [4].
Numerous biochemical and physical changes can occur in dairy products during manufacturing, distribution and storage processes due to ripening and degradation of nutrients in the products [1] [4]. Lipolysis and proteolysis are two major processes in dairy products ripening controlled by a variety of chemical, physical, microbiological, textural and rheological changes which take place under controlled environmental conditions [1] [4] [5] [6] [7] [8].
Sensory and flavor qualities of dairy products are significantly influenced by levels of peptides, amino acids and free fatty acids resulting from proteolysis and lipolysis [9] [10]. Proteolysis is the most important biochemical event, which gives a major impact on flavor and texture of most cheese varieties and other fermented dairy products [1] [4] [7] [11]. The rate of protein degradation is highly associated with the accessibility of proteolytic enzymes to the dairy product substrates, which is governed by the structure and configuration of the protein matrix of fermented dairy products such as cheese and yogurt [1]. Volatile compounds produced by lipolysis and proteolysis play major roles in flavor and sensory properties of yogurts [12] [13].
There are differences in lipolytic characteristics between goat and cow milk, due to the differences in fat moiety of the two species [1] [5]. Lipolysis and lipid oxidation are influenced by many factors, including free fatty acids, lipolytic microorganisms and enzymes, temperature, storage time, oxygen concentration, moisture content, antioxidant or pro-oxidant, etc. [1] [4] [14]. It has been shown that lipolyzed or rancid flavors are positively correlated to the levels of free fatty acid and short chain fatty acid contents. The presence of large amounts of free A. Siddique, Y. W. Park acids also can facilitate the rate of lipid oxidation [14].
Acid degree value (ADV) and peroxide value (POV) are two important indices for evaluation of lipid oxidation and lipolysis of food products. Elevation of POV or ADV during storage indicates deterioration of nutritional and sensory qualities of dairy products. Fortification of iron in milk and dairy products is desired due to the deficiency of iron in milk of many dairy species including cow and goats. Iron fortification in bovine milk cheeses in relation to lipolytic parameters and their correlations have been studied, while few such studies have been reported on caprine milk cheeses. Therefore, the objectives of this study were to: 1) determine acid degree value (ADV) and peroxide value (POV) of control and iron fortified caprine milk cheeses stored at two temperatures (4˚C and −18˚C) for 0, 2 and 4 months, and 2) evaluate correlation coefficients between ADV and POV of the experimental goat cheeses in relation to the extents of lipolysis and lipid oxidation of the products.

Preparation of Control and Iron Fortified Caprine Milk Cheddar Cheeses
Goat milk Cheddar cheeses were manufactured in three batches for CC, RFS and LMFS cheeses each using the standard procedure of cow Cheddar cheese processing [15]. and uniformly added to the cheese vat (Kusel Equipment Co. Watertown, WI), and agitated slowly for one hour. Thirty-five ml of single strength Chymax rennet (Chr. Hansen's laboratory, Inc. Hoersholm, Denmark) was added and stopped agitation for 30 -45 min for coagulation. The cheese curd was cut by wire curd knives (1/2" × 1/2" × 3/4") (Kusel Equipment Co. Watertown, WI).
Ten minutes after cutting, curds were cooked by gradual increase in temperature (1˚C every 5 minutes) to 39˚C for 30 minute. After cooking the curds, whey was drained, and cheese curds were stacked by two sides in the vat for Cheddaring process by turning over the curds every 15 min for 3 times.

Moisture
Moisture content for all samples in triplicates was analyzed by laboratory oven drying for 24 hours at 105˚C [17]. Moisture content of samples was determined by subtracting dry matter weight from the original total fresh sample weight.

Ash
The ash content of cheese samples was determined by using an AOAC procedure [17]. Two grams of cheese sample were weighed into chemically cleaned crucibles, then the crucibles were placed in a muffle furnace at 550˚C for eight hrs for complete ashing. After ashing, the crucibles containing ash samples were placed in desiccators to cool to room temperature, then the weight of ash measured with an analytical balance. The ash content was calculated by the following formula: Weight of ash g 100 Ash %, wet basis Weight of cheese sample g × =

Protein
The protein content was determined using a CEM Fastrac II analyzer (CEM cooperation, Mt. Laurel, NJ, USA), which is equipped with NMR technology, where the absorption of electromagnetic radiation in the radio-frequency region to measure N-C bonds in protein molecules of the cheese samples. The total protein content of the samples was assayed in triplicate.

Fat
The fat content of cheese samples was determined using the Babcock procedure [17]. Nine-gram shredded cheese samples were placed into Babcock Paley cheese bottles. Ten mL of hot (60˚C) deionized water was added to the bottle, and thoroughly mixed the samples were allowed to cool down to room temperature. Fifteen mL of sulfuric acid was added in portion-wise manner (8, 4 and 3 mL) by swirling each time after careful addition. The bottles were shaken on a mechanical shaker for at least 5 minutes, and then place in a 60˚C centrifuge for 5 minutes at 600 rpm. The bottles were removed from the water bath at 57˚C, and dried quickly. The fat was measured immediately from the bottom of the lower meniscus to the highest point of upper meniscus of the graduated neck of the bottle.

Acid Degree Value (ADV)
ADV was determined according to the procedure of Richardson [18].

Peroxide Value (POV)
Peroxide value was analyzed using the AOCS procedure [19]. The lipids of cheese samples were extracted using Folch et al. [20] method. Five grams of previously extracted fat sample was weighed into a 250 mL Erlenmeyer flask. Thirty milliliters of acetic acid-chloroform solution (3:2 v/v) was added to each sample, and contents swirled until dissolved. A 0.5 mL saturated potassium iodide was added to each sample, and shaken for one min. Thirty milliliters of distilled water was added to each sample, and the sample was shaken vigorously. One mL starch solution (1%) was added to each sample. The sample flask was titrated with 0.01 N sodium thiosulfate until the bottom layer appeared milky, which indicated the end point.
The peroxide value was calculated using the following equation: as lactic acid, organic acids and free fatty acids are generated in the aged cheese samples as the storage period advanced. The acid degree values in Table 2 also showed the increasing trend in all the experimental goat cheese samples at the 4 months of storage period. However, beyond 4 months storage, the decreases in pH may not continue due to the buffering components such as ammonia group would be generated from the ripening cheese proteins for further ripening of the cheese products.

ADV (Acid Degree Value)
ADV is a measure of the amount of free fatty acids generated in a food sample for a certain period of time.
The ADV of fresh control cheese and two types of iron fortified cheese samples for 0, 2, and 4 months are summarized in Table 2.
The ADV values at 0 and 4 month at 4˚C for control, RFS and LMFS cheeses were: 0.67, 0.73, 0.64; 1.24, 1.78, 1.58, respectively, indicating that significant (P < 0.01) elevations occurred in ADVs of all three cheeses after 4 months storage, while the differences in ADV between cheese types were not significant at 2 months of storage. The effect of storage temperature (4˚C and −18˚C) was also significant (P < 0.05) especially at 4month storage ( Table 2 and Table 3). Increases in ADV values in this study are in agreement with the previous reports on goat milk cheeses [1] [5]. The 2-way interaction effects were significant on ADV values by storage period x temperature (P < 0.01) and cheese type x storage period (P < 0.05). These ADV results imply that storage time and temperature, and their interactions had significant influence on lipolysis of the experimental goat cheeses. ADV values of LMFS and RFS cheeses were higher than those of control cheese at 4 months storage, which may indicate that the added iron may have increased the amount of free fatty acids compared to the non-iron fortified control cheese. The 3-way interaction of cheese type × storage time × temperature effect was not significant on ADV, but significant (P < 0.05) on pH and POV in this study (Table 3).

Peroxide Value (POV)
Peroxide   values of the control and iron fortified goat milk Cheddar cheeses during four months of storage are shown in Table 4 and Figure 1.
There were significant (P < 0.05) differences in POV between storage periods for the control and iron fortified goat Cheddar cheeses (Table 4 and Figure 1).
Cheeses stored at frozen temperature (−18˚C) at 4 month storage showed slightly low peroxide value than those samples stored at refrigerated temperature (4˚C), suggesting that the cheese samples stored at higher temperature may have a tendency to cause more lipid oxidation than those stored at lower temperature.
Samples at 4 month storage had significantly (P < 0.05) higher peroxide values, compared to 0 and 2 month stored ones, implying that the rate of lipid oxidation can increase as the storage time extended for the goat milk Cheddar cheeses.
However, the POV values observed in this study were still below the critical value of peroxide less than 1 milliequivalent peroxide/1000 g sample for fresh fat [21], indicating that the experimental goat Cheddar cheeses had no appreciable lipolysis up to 4 months storage, so that the quality of the cheeses would be acceptable for consumption. Means with different superscript within a same row are significantly different (P < 0.05); x,y,z Means with different superscript within a same column are significantly different (P < 0.05).

Correlation between ADV and POV
It is generally known that ADV is the index for lipolysis and POV depicts for lipid oxidation of animal food samples. In the study of correlation(r) between ADV and POV in dairy products, it would be expected that a positive strong relationship would exist between the two parameters in the aged cheese or other dairy products. The r values between ADV and POV for the pooled data of three types of goat cheeses across storage period and across storage temperature were significant (P < 0.05 or P < 0.001) ( Table 5). The outcomes of the present study revealed that the ADVs had significant positive correlations with the POVs of the three types of goat Cheddar cheeses stored both 4˚C and −18˚C for 4 months storage period. These results may suggest that there were significant correlations