Abstract: The present study is a trial for processing gariss (Sudanese camel fermented milk) in the laboratory and to investigate the effect of pasteurization and storage conditions on its microbial content. Gariss that was used as a culture for fermentation showed total bacterial count of 1.8 x 106, Lactobacillus spp. count of 4.9 x 106 andyeast count of 4.9 x 106. Pasteurization and storage periods revealed significant variations (p<0.05) for total bacterial count. Similarly, Lactobacillus spp. count was found to show significant (p<0.05) variations by the incubation temperatures. Also the storage conditions (temperature and duration) revealed significant differences (p<0.05) between the processed samples for yeast count. The processed samples were found to show shelf life of up to 10 days. The present study concluded that the microbial contents were affected by pasteurization and storage conditions (temperatures and storage periods). Hence the study recommended that more investigations are needed on the microbiological properties of camel`s milk products.
Introduction
Numerous microorganisms, including bacteria, yeasts and molds, constitute the complex ecosystem present in milk and fermented dairy products (Ogier et al., 2004). The microorganisms that responsible about lactic acid and alcoholic fermentation are lactic acid bacteria (Attia et al., 2001). These microorganisms are commonly found in a symbiotic relationship in many fermented milks of the world (Dirar, 1993).
Lactic acid bacteria (LAB), especially the genus Lactobacillus, followed by Enterococcus, Lactococcus and Leuconostoc, dominated the microflora of kule naoto, the traditional fermented milk products of the Maasai in Kenya (Mathara et al., 2004). They also added that the major Lactobacillus species was Lactobacillus plantarum (60%) and a lower frequency of isolation for Lactobacillus fermentum, Lactobacillus paracasei and Lactobacillus acidophilus.
The microflora involved in production of suusac, a Kenyan traditional fermented camel milk product, were enumerated and identified and a total of 45 LAB and 30 yeast isolates were isolated from the 15 suusac samples. The LAB species were identified as Lactobacillus curvatus, Lactobacillus plantarum, Lactobacillus salivarius, Lactococcus raffinolactis and Leuconostoc mesenteroides subsp. mesenteroides. The isolated yeasts were identified as Candida krusei, Geotrichum penicillatum and Rhodotorula mucilaginosa (Lore et al., 2005). Similarly Shuangquan et al. (2004) studied the microflora in traditional fermented camel's milk, Hogormag which is made by nomadic families in the Inner Mongolia Autonomous Region. They identified the isolated lactic acid bacteria as Enterococcus faecium, Lactococcus lactis subsp. cremoris, Leuconostoc lactis, Lactobacillus acidophilus, Lb. helveticus and Lb. plantarum and Lb. bavaricus. The yeasts that were isolated were identified as Candida kefyr, Saccharomyces cerevisiae, C. krusei and C. glabrata. However, Robinson (1981) indicated that in the dairy industry Lact. bulgaricus, Lact. lactis, Lact. acidophilus, Lact. helveticus, Lact. caseii and Lact. plantarum are most commonly used organisms. Similarly Gobbetti et al. (2000) mentioned that Lactobacillus delbrueckii subsp. bulgaricus and Lact. lactis subsp. cremoris are two of the most widely used industrial strains which are used as starters for fermented milks and several types of cheeses. Moreover, Robinson (1981) mentioned that Str. thermophilus is used symbiotically with Lactobacillus bulgaricus as a yoghurt and cheese starter culture.
Yagil (1982) indicated that fermented products of camel’s milk have various names in various parts of the world. In the Sudan gariss is special kind of fermented milk, prepared solely from camel’s milk under more or less continuous shaking (Dirar, 1993).
Gariss fermentation is attributed to lactic acid bacteria and alcohol producing yeasts (Mirghani, 1994). Gariss thus falls in the family of acido-alcoholic fermented milks that include kefir and koumis (Dirar, 1993). He also indicated that the direct microscopic observations of gariss samples obtained from Butana area and Northern Kordufan Province revealed two types of microorganisms, which are lactobacilli and yeast. Also a limited numbers of streptococci are found as he reported.
The aim of the present study is processing of gariss in the laboratory after heat treatment using a ready starter gariss, in order to assess the microbial content of the processed samples and to assess its shelf life.
Materials and Methods
Sources of Samples
The present study was conducted during the period from January to April
2004. Fresh milk for preparation was obtained from Khartoum North (Elhag Yosif
area). Half of the quantity of the camel milk (1250 mL) was pasteurized at 63°C
for 30 min, as mentioned by Attia et al. (2001). Acidification of the
raw fresh and pasteurized milk was carried out by the addition of 50 mL fractions
of a ready gariss that obtained from Elhag Yosif area as a culture. After inoculation
each of the sample was divided into 625 mL fractions, 312.5 mL fractions (pasteurized
and non pasteurized gariss samples) were incubated at the room temperature about
25°C and the other was incubated at 37°C.
Analysis of the Samples
The analysis was done at the laboratory of the Department of Dairy Production,
Faculty of Animal Production of University of Khartoum. The prepared gariss
samples were examined for total bacterial counts, Lactobacillus spp.
counts, Streptococcus spp. counts and yeast counts. The microbial counts
were carried out after one hour from inoculation, 3, 18 and 42 h. The counts
were then done periodically each 48 h for 10 days.
Sterilization, serial dilution and preparation of the media were done according to Harrigan and MacCance (1976). Standard plate count agar and Malt extract agar were used for total bacterial count and yeast counts, respectively (Harrigan and MacCance, 1976). Lactobacillus spp. count was determined on MRS agar and the count of Streptococcus spp. was determined on M-17 agar (Attia et al., 2001). Isolation and identification of the purified colonies was carried out according to Harrigan and MacCance (1976) and Barrow and Felthman (1993).
Statistical Analysis
Experiment was conducted using Completely Randomize Design. The analysis
of variance and the significant differences between means were determined using
Duncan Multiple Range test using SPSS.
Results
Microbial Content of Processed Fermented Camel Milk Samples
The acidity and pH of the gariss culture was found to be 2.49% and 3.8,
respectively. The total bacterial count, Lactobacillus spp. count and
yeast count of the gariss culture were found to be 1.8x106, 4.9x106
and 4.9x106, respectively. However, the fresh camel milk, which
collected for the processing was found to have acidity and pH of 0.12% and 6.4,
respectively.
Microbial Content of the Processed Gariss Samples
Log Total Bacterial Counts
Table 1 showed that after one hour incubation the mean
log total bacterial count revealed values of 4.1±0.001, 4.41±0.006,
4.36±0.011 and 4.54±0.027, respectively. At 186 and 234 h the
reduction of means log total bacterial counts of the samples were recorded.
However, at the end of the storage period (234 h) the mean log revealed values
of 6.24±0.011, 6.69±0.012, 6.48±0.02 and 6.76±0.003,
respectively.
Table 1 also showed significant differences (p<0.05) between gariss samples made from pasteurized milk and that made from non pasteurized milk. However, it revealed significant variations (p<0.05) between the samples during the different storage periods.
Log Lactobacillus spp. counts
The mean Lactobacilli spp. counts in gariss samples made from pasteurized
milk that incubated at both 25 and 37°C and gariss samples made from non
pasteurized milk that incubated at 25 and 37°C after 1 h incubation were
found to be 3.24±0.088, 3.68±0.324, 3.58±0.032 and 3.71±0.012,
respectively (Table 2). The same table also showed gradual
increase in the Log Lactobacillus spp. counts in 5 h of the storage period.
After 42 h incubation, gariss samples were found to be 5.1±0.011, 5.76±0.018,
5.44±0.033 and 5.53±0.029, respectively. The average reduction
in the log Lactobacillus spp. was recorded at 186 and 234 h of incubation.
The mean log Lactobacillus spp. counts at 234 h incubation were found
to be 5.45±0.081, 5.99±0.000, 5.21±0.63 and 6.28±0.014,
respectively.
| Table 1: | Comparison of log total bacterial counts of the processed gariss samples made from pasteurized and non pasteurized camel milk incubated at different temperatures for 234 h |
| In this and the following tables: Different superscript letter(s) on the same column and raw indicated significant differences at p<0.05 | |
| Table 2: | Comparisons of log lactobacilli counts of processed gariss samples made from pasteurized and non pasteurized camel milk incubated at different temperatures for 234 h |
| Table 3: | Comparison of log yeast counts of the processed gariss samples made from pasteurized and non pasteurized camel milk incubated at different temperatures for 234 h |
Moreover, the higher increase was observed in the mean log Lactobacillus spp. count of gariss samples made from non pasteurized milk that incubated at 37°C. However the lower rate was recorded for gariss samples made from pasteurized milk which incubated at 25°C. Table 2 also revealed significant variations (p<0.05) between gariss samples made from pasteurized and non pasteurized milk which incubated at 25°C. Moreover, gariss samples made from non pasteurized milk that incubated at 37°C revealed significant differences (p<0.05). However, non significant variation (p>0.05) were found when comparing gariss samples made from pasteurized and non pasteurized milk which incubated at 37°C.
Log Yeast Counts
Table 3 showed variations in the increasing rate of the
means log yeast counts. Gariss samples made from pasteurized milk that incubated
at 25°C revealed the lower mean log counts. However, higher mean values
were recorded for gariss samples that made from milk, which incubated at 37°C.
The data also revealed that the means log yeast counts for gariss samples were
3.48, 3.828±0.002, 3.67±0.039 and 4.23±0.047, respectively.
Moreover, the means log yeast count after 42 h of storage reached values of
5.36±0.011, 5.8866±0.01204, 5.7416±0.05421 and 5.8863±0.01765,
respectively. At the end of the storage period (234 h) those samples revealed
means log yeast counts of 5.8781±0.09216, 6.2607±0.0008425, 6.037±0.02678
and 6.432±0.003688, respectively. Table 3 also showed
significant variations (p<0.05) due to pasteurization and storage conditions.
Discussion
The microbial content of processed gariss revealed that the total bacteria count showed minimum rate of growth at the beginning of the incubation. This supported Attia et al. (2001) who reported that the activity of the starter in dromedary milk was characterized by a longer lag phase (approximately 5 vs. approximately 1 h) and by an earlier decline phase than bovine milk. This might occur due to the presence of growth inhibiting– factors in the camel’s milk (Gran, 1991; Attia et al., 2001). The present results also showed that both pasteurization and incubation temperature affected the total bacteria counts. Since the lower mean values were recorded for gariss samples made from pasteurized milk that incubated at 25°C (Table 1). These results were in agreement with the IDF (1994) and Harding (1999). Also IDF (1994) stated that in the manufacture of milk based products, a heat treatment process may perform a technological function, for example to increase heat stability and prevent syneresis. The procedure of heat treatment if introduced to camel owners who process those traditional products, it would improve their product by killing the pathogenic microorganisms and increasing the shelf life (Harding, 1999) and hence safe product could be commercialized.
The Lactobacillus spp. counts revealed the same pattern of the total bacteria count at the beginning of the storage periods, since they revealed along lag phase (Table 2). This was in accord to the previous findings of Attia et al. (2001) that the activity of the starter in dromedary milk was characterized by a longer lag phase. However yeast counts (Table 3) showed high rate of increase at the beginning of the incubation than the Lactobacilli spp. counts. The source of yeast in Gariss prepared during the present study was the starter Gariss as in the present study we use the traditional starter from the nomadic owners who supplied the camel milk. Yeasts are present in indigenous African fermented milks in numbers up to log 8 cfu g-1, together with a varied Lactic Acid Bacteria (LAB) flora and therefore potentially contribute to product characteristics (Narvhus and Gadaga, 2003).
The processed gariss samples were found to have a high keeping quality, since the shelf life of the product was extended up to 234 h at both 25 and 37°C. The processed gariss samples revealed longer shelf life than yoghurt which revealed a shelf life of 10 days when kept under refrigeration (Robinson, 1981). The variations in the shelf life between the two products might occur due to the presence of antibacterial and antimicrobial agents in the camels’ milk (Elagamy, 1992). Moreover, pasteurization of the milk had an effect on the keeping quality of the product, since the heat treatment is used to kill the pathogens and to extend the storage life of the products (Harding, 1999). The significant rate of increase for the total bacterial counts, Lactobacillus spp. counts and yeast counts and their significant decrease at the end of storage periods indicated a prolonged keeping quality and that minimum spoilage organisms are present. The spoilage of the product was found to occur after 234 h of incubation period in the two storage temperatures (25 and 37°C). The spoilage of the non pasteurized fermented camel’s milk might occur due to the presence of lower initial numbers of contaminated yeast.
The present study concluded that pasteurization and fermentation improve the quality of camel milk, since gariss revealed longer shelf life in the different storage conditions which used. The high temperature (25 and 37°C) used during this study might be more or less similar to the storage condition of the traditional gariss (kept in a leather bags at the back of one of the camel). Hence it is recommended that heating of milk prior to its processing into any dairy products should be introduced to camel herders. Also establishment of mobile dairy factory for processing of pasteurized camel milk and fermented products is urgently needed. Further research is needed to address the fermentation process of camel milk with special references to the microbial content and its properties. Isolation, identification and molecular characterization of fermentative microorganisms, which found in the camels milk products comparing with the other microorganisms present in other animal milk products is urgently needed.