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Effect of pasteurization of milk on the keeping quality of fermented camel milk (Gariss) in Sudan

E M El Zubeir Ibtisam and I Ibrahium Marowa

Department of Dairy Production, Faculty of Animal Production, University of Khartoum, P. O. Box 32, Postal code 13314, Khartoum North, Sudan
Ibtisammohamed@hotmail.com

The results of this research have been presented as a poster presentation at the International Conference on Traditional Dairy Food, Karnal, India, November 2007

 

Abstract 

The present study was carried out during the period of April to May 2005 with the aim of improving the traditional fermented camel milk (Gariss) that produced by the camel owners in pastoral areas of Sudan. The pasteurization of milk and refrigeration storage of the processed Gariss was evaluated.

 

The processed Garris samples from non pasteurized and pasteurized camel milk showed mean values for fat content of 3.0 0.445% and 3.0 0.076%, respectively. The protein contents were found as 3.1 .14% and 3.2 0.311%, the ash values were 0.64 0.108 and 0.71 0.067% and the total solids were 9.6 0.445% and 10.0 0.801%, respectively. Similarly the maximum and minimum values of these measurements were reported. Variations in developed acidity and the pH were plotted during incubation periods (18 hours) and storage periods (18 days) for Garris made with pasteurized and non pasteurized milk. The present study revealed that the shelf life or the keeping quality of Gariss from non pasteurized milk (10 days) was less than those obtained for Gariss made after pasteurization of milk (17 days) when stored at refrigeration temperature.

 

Hence it is concluded that pasteurization and refrigeration of camel fermented products will improve the keeping quality of the products and extending the shelf life, which could be of beneficial uses as future industry.    

Key words: Chemical composition, Gariss, processing, storage, refrigeration, shelf life


Introduction

In rural areas of Sudan, there are many milk producing animals and with surplus of milk, where there is no marketing systems, therefore milk spoils if it is not processed. The surplus milk produced is fermented by souring it into one or other certain dairy products, some of which are spread wide in the country, whereas other are confined to certain geographical niches (Abdel Gadir et al 1998).

 

Fermented milks have been claimed by some research findings for being more nutritious and health promoting than fresh milk (Perdigon et al 1995 and El Zubeir et al 2005). In the earlier days, fermentation was used to control the growth of harmful bacteria and some pathogens while making indigenous milk products, moreover the fermented milks are the most common products from which other dairy products are also made (Thapa 2000).

 

During the lactic fermentation process, dromedary milk showed behaviour different from that of bovine milk at the microbiological, biochemical and structural levels that are certainly due to intrinsic factors (Attia et al 2001). In fact the coagulation caused by lactic fermentation did not produce a curd but simply flakes that lack firmness and that were unable to undrgo further technological treatment (Abu- Tarboush 1994). Similarly Attia et al (2001) reported that fermented dromedary milk did not produce a curd structure but few dispersed small casein fragments at the surface and a film or firm gel at the bottom of the vessel. Garris is fermented camel milk of Sudan, which is not always available for the family as camels are often driven away in search of pastures (Dirar 1993 and Abdel Gadir et al 1998). The fermentation of Gariss takes place while the camels are in move, due to the inherent jerk in the camel’s walk; the milk in the bags is gently shakes during fermentation (Mirghani 1994).

 

Pasteurization is adequate for public health assurance of milk safety provided that good manufacturing practices are followed (Holsinger et al 1997). Camel milk is more heat resistant than those in cow milk, which is advantageous in commercial production of camel milk products (Wernery et al 2003). Moreover camel milk antimicrobial factors were significantly (P≤0.01) more heat resistant than cow and buffalo milk proteins (Wernery et al.  2005). Hassan et al (2006) found pasteurization of camel milk before its fermentation into Gariss improved the microbiological content and increasing the shelf life o the product.

 

The present study is a trial for processing Gariss in the laboratory and to study the effect of pasteurization and refrigeration storage on the shelf life of the processed product.

           

Materials and methods 

Source of camel milk

 

The camel milk samples were brought from El Geraif that located in Eastern Nile Province of Khartoum North (Khartoum State) during the period of April to May 2005, after contacting one of the camel’s owners to supply both camel milk and Garris samples that to be used as starter for processing Gariss in the laboratory. The camels were of indigenous breed that fed extensively throughout the year.

 

Processing of Garris

 

Nine litres of fresh raw camel milk (in duplicate) were brought to the Dairy Processing laboratory of the Department of Dairy Production, Faculty of Animal Production, University of Khartoum. The camel milk samples were divided into 6.5 litres, which was pasteurized at 63 C for 30 minutes according to Attia et al (2001) and 2.5 litres that was processed with out any heat treatment. Then to both samples the starter was added at a rate of 3%. Both samples were divided aseptically into clean sterile bottles (250 ml) and incubated at 37 C for 24 hours and then kept at the refrigerator (8 C) to estimate the shelf live of the product.

 

Chemical analysis

 

The percentage of fat was determined using Gerber methods, protein was done using the Kjeldahl methods, total solids was done using dry oven method and ash was done using the muffle furenes for fresh camel milk, the starter Garris and the processed Garris (Bradley et al 1992). Similarly acidity and pH values were estimated using the methods of Bradley et al (1992). 

 

Statistical analysis

 

Descriptive analysis was done to assess fat, protein, total solids, ash and acidity % using SPSS program (Statistical Package for Social Science).version 10. Moreover the acidity and pH were plotted graphically to show their effect on the keeping quality and the shelf life of camel milk using the same program. 

 

Results 

The chemical composition of the fresh and the Gariss that used as starter during the present study were shown in Table 1.


Table 1.  Comparison of compositional quality of the fresh camel milk and starter Gariss used for preparing fermented camel milk

Items

Fresh milk

Starter Gariss

Fat %

3.4

4.3

Protein %

3.6

3.3

Ash %

0.65

0.86

Total solids %

10.1

10.7

Acidity %

0.20

1.07

pH

6.5

4.2


The average values of protein and total solids contents from Gariss made after pasteurization of camel milk revealed higher values for means and the maximum levels than those from non pasteurized camel milk (Table 2).


Table 2.   Effect of pasteurization on composition of camel fermented milk (Gariss)

Items

Non pasteurized milk

Pasteurized milk

Maximum

Minimum

Mean+ Sd

Maximum

Minimum

Mean+ Sd

Fat %

3.1

2.8

3.0 0.45

3.1

2.9

3.0 0.08

Protein %

3.4

2.8

3.1 0.14

3.6

2.8

3.2 0.31

Ash %

0.76

0.51

0.64 0 .11

0.86

0.56

0.71 0.067

Total solids %

10.3

9.8

9.6 0.45

10.7

9.2

10.0 0.8


Similarly the ash contents revealed higher values for means, minimum and the maximum levels than those from non pasteurized camel milk as shown in the same table. However similar values for fat level were reported for the processed Garris samples from non pasteurized and pasteurized camel milk (Table 2).

 

The development of the acidity for Gariss from both pasteurised and non pasteurized milk during the incubation of Gariss as shown in Figure 1, revealed slow development up to 7 hours.


 
Figure 1.   Development of acidity of Garris samples during the incubation (37 C)


Then both Gariss showed higher increase and they reached more than 1.2% at 18 hours of incubation. Moreover higher values were estimated for pasteurized milk compared to those from non pasteurized milk (Figure 1). Similarly Gariss made from pasteurised camel milk revealed more or les similar degree of acid development until day ten of the storage periods and after which it decreases up to day 18 of the storage (Figure 2).


 

 
Figure 2.
  Development of acidity of Garris samples during storage (8 C)


These values were also higher than those estimated for Gariss made from non pasteurized milk except at day nine and day ten, which was the last day of the shelf life. However sudden increase was observed for the acidity on the third and ninth day of the storage for Gariss made from the non pasteurized milk (Figure 2) indicating the spoilage of the product. On the other hand the pH of Gariss from non pasteurized milk showed a sharp increase at day four followed by a sharp decrease at day six, then continued slowly until day tenth of the storage period (Figure 3).


 

 

Figure 3.  Development of pH of Garris samples during storage (8 C)


On the other hand Gariss made from pasteurized milk showed slow increase for the pH values up to day six and then regular slow decrease till day ten of the storage period. However a sharp increase was noticed again at day twelve and then slow decrease was observed until day 16 (Figure 3) indicating a shelf life or keeping quality of 17 days as shown in Figure 3. 

 

Hence the shelf life or the keeping quality of Gariss from non pasteurized milk (10 days) was less than those obtained for Gariss made after pasteurization of milk (17 days) as shown in Figure 2 and Figure 3.

 

Discussion 

The milk samples used during the present study (Table 1) for Gariss preparation showed different values for protein, lactose, fat, total solids and ash, while higher acidity than those reported by Mehaia (1993), Saima et al (2003) and Hassan et al (2007). This supported the previous report of Ramet (2001) who added that the dry matter content of camel milk varies according to the origin of camel milk and that the dry matter, fat and protein content of camel milk were lower than that of cow’s milk.

 

Higher level of camel milk acidity used during the present study was found than that reported by Saima et al (2003). This might be due to the lake of proper handling and hence contamination by microorganisms as most of camel owners practiced less hygiene during milking and storage of their milk (Shuiep, 2006). The lack of the cooling facilities might be another cause of this high acidity which is also influence the growth of fermentative microorganisms in milk (Dirar 1993). This lower acidity might be also the reason of lower compositional content of camel milk, which suggesting the urgent need of structuring proper marketing channels for camel milk supported by cooling and pasteurization facilities. Since most of the camels are located in the dry and semi dry areas, which is far away from consumption areas. This was in accord to Bellow et al (2007) who reported that the storage temperature is the one of important parameter that affects the spoilage of milk.  On the other hand Gariss that used as starter during the present study (Table 1) showed higher fat, total solids, ash and pH and lower protein content and acidity than that used in the previous study carried out by Hassan et al (2007). This might also reflect the variations of the compositional content of camel milk used and the way of preparing and preserving the starter by camel owners. Dirar (1993) mentioned that some may leave it for months in dry state and just add their milk when ever available.

 

The average values of protein content from Gariss made after pasteurization of camel milk revealed higher values for means and the maximum levels than those from non pasteurized camel milk (Table 2). These results were in agreement with Farah (1996) as he reported that the pasteurization does not affect the chemical composition of camel milk. The minimum values obtained during the storage might be due to the effect of the fermentative organisms (Harding, 1999). Also the lower minimum levels of protein of Gariss during the present study might be due to the increase of proteolytic activity during fermentation of camel milk (Attia et al 2001). This is because of the relatively high β casein content of camel milk (Kappeler et al 1998). Similarly the variations of the chemical composition of Gariss due to pasteurization process supported Hassan et al (2007). However Wernery et al (2005) reported that the reduction in vitamin C concentration following pasteurization of camel milk was minimal and this could be considered as tremendously advantageous for the consumer in arid and semi-arid countries where vitamin sources are scarce. Moreover Mirghani (1994) reported that fermentation causes significant increase in the free amino acids content and liberation of significant amount of peptides.

 

The increase in the lactic acid (acidity) level was started gradually at the beginning of incubation and storage period (Figure 1 and Figure 2). This increase was accompanied by decreasing in pH levels (Figure 3) which was similar to Attia et al (2001). However longer lag phase (7 hours) was obtained during the present study compared to 5 hours obtained by Attia et al (2001). Moreover they reported that lactic acid fermentation lower the pH, altering casein micelles, minerals, caseins and salvation. The results of those modifications are the destruction of the micellular structure and the formation of the three dimensional network or coagulum, which encloses all the aqueous phase. The lower rate of those changes especially at the beginning of incubation and storage periods might be due to the presence of the inhibiting factors in the camel milk (Elagamy 2000; Attia et al 2001 and Benkerroum et al 2004). Gariss from pasteurized milk showed higher pH and lower acidity than those from non pasteurized samples which supported Gassem and Abu-Tarboush (2000). They found that the pH of whey samples decreased with increasing fermentation time until 12 hours and then it remained constant, on the other hand, titratable acidity increased with increasing fermentation time and both sweet camel whey and acid camel whey had the highest acidity (1.31% and 1.30%, respectively) compared to those from cows milk. This might also be due to pasteurization of milk that showed an effect on the keeping quality of the products, since the heat treatment is used to kill the pathogens and to extend the storage life of the products (Harding, 1999). Similar observation were obtained by Attia et al (2001) as they found the maximum acidification rate of dromedary milk was 12 hours compared with 6 hours for cow’s milk at 37 C.

 

Gariss from pasteurized camel milk showed high keeping quality, since it revealed a shelf life of 17 days at 8 C compared to those from non pasteurized camel milk that showed a shelf life of 10 days at 8 C. The improvement of the keeping quality compared to those reported by Hassan et al (2007) as they obtained about 234 hours (about 9 days) might be due to the different incubation temperature as they kept the processed Gariss at 25 C and 37 C. Also the spoilage action that occur might be due to the presence of lower initial numbers of contaminated yeast, which have ability to thrive in fermented milk at pH as lower as 1.5 as even for Gariss that used after pasteurization of milk, the starter used was obtained from the camel owners and it was not pure culture, as it was meant to improve the traditional way of fermented camel used among those nomadic tribes. However Attia et al (2001) when used pure culture that used for cows’ milk, they concluded that dromedary milk appear less favourable for the lactic fermentation because the activity of the inoculated lactic starter was lower in this milk than in bovine milk.

 

Hence this study concluded that higher keeping quality of longer shelf fermented milk product can be produced from camel milk using heat treatment and stored at refrigeration. it is suggested that further work should be carried out trying to obtain and develop pure starter cultures from traditional Gariss in order to market them nationally, regionally and internationally.

 

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Received 5 February 2008; Accepted 30 March 2008; Published 1 February 2009

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