Microbial load and acidity along the suusa value chain
Kenya Bureau of Standards (KEBS) regards raw whole camel milk as good when the total viable counts (TVC) are between 0-5 × 105 cfu/ml for grade I and II (KEBS, 2007). The raw camel milk at production was above the recommended range and therefore, the milk can be regarded as of poor quality. High TVC at production can be attributed to handling practices like not washing hands before milking, no washing of the camel’s udder before milking, use of plastic containers for milking and storage of milk in plastic containers which are not easy to clean. Use of recycled plastic containers which are not easy to clean harbours spoilage microorganisms, unrefrigerated transportation, long distance, poor roads to cooling centres and pooling of milk from different suppliers at the cooling centres are risk factors to the growth and multiplication of the indigenous microflora, resulting in reduction of milk quality and safety (Wayua et al., 2012).There was significant increase(P < 0.0.5) in TVC from production to marketing which is attributed to absence of heat treatment of milk prior to fermentation coupled with spontaneous fermentation. Results agree with those reported by Odongo et al. (2016) and Matofari et al. (2013). The GNR were the most prevalent types of microorganisms for both the intended and unintended suusa while the YM were the least prevalent for both.
Lactic acid increased significantly (P < 0.05) from production to the market with no effect on microbial load reduction as shown in Figs. 4 and 5.With fermentation, lactic acid bacteria break down lactose into lactic acid. Presence of GNR which are fermentative organisms had an influence on increased acid content. Intended suusa is fermented over a period of 3 days (72 hrs) and this further explains why the percentage lactic acid was higher than unintended suusa which takes less than 24 hours.
Coliforms increased significantly (P < 0.05) from production to the market by 1 log increase as shown in Figs. 2 and 3. Coliforms are found in the soil, mud, dust, plant materials and can be dispersed into the atmosphere by dust into the product. With natural fermentation, the coliforms will multiply and cause problems in the final product because lactic acid bacteria will initially be very low Gadaga et al. (2004). Coliforms also have adaptation strategies that range from temperature evasions, acid tolerance and production of probiotics like colicins that inhibit growth of other microorganisms (Abee et al. 1995; Gadaga et al., 2004). Occurrence of coliforms more so E.coli in the final product despite high lactic acid (Figs. 4 and 5) is probably due to induced acid tolerance by the organism through production of acid shock proteins which enhance its survival through neutralization of the external environment, adjusting catabolism to the new environment, performing DNA repair and membrane biogenesis and contribute to microbial pathogenesis (Bearson et al., 1997). Karagözlü et al. (2007) found that stationary phase cells of E.coli strains were able to survive and multiply in kefir (Caucasian fermented camel milk). It has also been found to survive in fermented goat milk, amasi (Bearson et al., 1997). Isolation of coliform bacteria along the suusa value chain is an indication of presence of enteric pathogens in the suusa value chain as shown in Table 5. This shows hygienic conditions during handling and processing of camel milk into suusa are low. Suusa therefore has public health risk potential for spread of foodborne illnesses such as Escherichia coli O157:H7 illnesses.
There was a significant (p < 0.05) increase in spore counts from production to market samples by 3 log increase as shown in Figs. 2 and 3. Spore forming bacteria are environmental microorganisms such as Bacillus and Clostridium species. At production, they may originate from water used to wash the milking equipment and dust from the milking area. Spore formers like Bacillus cereus display a mechanism of acid tolerance response (ATR) and can survive below pH 4.0 favourable for spore formation (Gadaga et al., 2004). This explains the existence of increased spore forming bacteria in suusa at the market level. Gram positive spore forming rods were identified as Bacilli. High incidence at the market could be attributed to the marketing environment characterised by sale in the open with heaps of waste material, dust and mud close to where the product is sold. Spores are carried by wind into the atmosphere and into the product. Bacilli are aerobic whose typical habitat is soil although they are widely distributed in nature and gain access to milk and suusa through air, water, fodder and feed. Spore-forming bacteria are known to cause food spoilage and food-poisoning by producing heat labile enterotoxins. Therefore, their presence in suusa poses a risk of food poisoning by the enterotoxins to the consumers of the milk product.
Yeast and moulds increased by 1 log increase from production to the marketas shown in Figs. 2 and 3. High contamination by yeasts and moulds may be due to poor processing and marketing conditions and uncontrolled fermentation which led to contamination. During spontaneous fermentation of suusa, organic acids such as lactic, acetic and propionic acids are produced which lower the pH. The lower pH is favourable for growth of yeast and mould species which causes these species to become competitive in the immediate medium (suusa) hence the significant increase (P < 0.05) in yeast and mould count in marketed suusa (Lefoka, 2009).
Results in Tables 3 and 4 display the main type of microorganisms that were isolated from intended and un-intended suusa along the value chain. Gram negative rods had the highest incidence of 88 % from production to the market followed by Gram positive cocci with an incidence of 84 %. Micrococci were isolated and could account for the high count of Gram positive cocci which is mostly found in water, soil and dust. Yeast and moulds had the least incidence at 28 %. Gram negative rods were identified to be E. coli, Pseudomonas and Enterobacter. Presence of E.coli is an indication of faecal contamination by handling from production to the market Rochelle-Newall et al. (2015). This indicates possibility of presence of other enteric pathogens. Gram positive spore forming rods were identified as Bacillus and the high incidence at the market could be attributed to the environment in which the product is produced and sold. The environment was characterised by heaps of waste material, dust and mud and this could be the source of the spores which are carried into the atmosphere and into the product.
Gram positive cocci isolated from camel milk and suusa included Streptococcus and Micrococcus species. Streptococcus species especially the Streptococcus lactis group originate from equipment that is contaminated due to insufficient sanitation. Organisms like Micrococci, coliforms and enteric pathogens originate from hand milking and milk handling that might contaminate the milk via the skin, nose and mouth(Cui et al., 2016). Risk factors identified in the field of study that have contributed to the specific organisms associated with suusa were: not washing hands or camels’ udder before milking, dusty milking environment, use of organoleptic tests for quality assessment of milk, bulking milk from different suppliers, use of not easy to clean plastic containers, delayed milk delivery, lack of refrigeration during transport and sale of suusa in open air markets (Noor et al., 2013). Other authors (Akweya et al. 2012; Wanjohi et al. 2010) have also detected Staphylococcus aureus, in camel milk.
Spores of Bacillus species as well as the organism were also detected. The genus Bacillus are typical habitats of the soil and are widely distributed in nature and may gain access to milk and dairy products through the air, water, fodder and feed thereby present on the skin and hair of cattle (Loralyn and Robert, 2009). Bacillus species produce heat stable protease and lipase which may eventually cause spoilage to camel milk and milk products (Samaržija et al. 2012). Other species such as Bacillus cereus produce toxins which lead to food intoxication from ingestion of contaminated food. Presence of the Bacillus species in camel milk makes the food a potential risk to consumers. Spores increased significantly (P < 0.05) along the value chain in Fig. 2. This is attributed to handling practices observed along the value chain that have led to contamination of both raw and fermented product. Risk factors identified include: dusty milking environment, use of plastic milking and storage containers and unrefrigerated transport of raw milk from production to cooling centres. These factors most probably led to the growth and multiplication of spore forming bacteria hence high counts.
Among the major isolates of the microorganisms was the Pseudomonas species. Pseudomonas species produce heat stable proteases and lipases keeping their activity even after pasteurization thereby producing off-flavours in milk as well sweet curdling of pasteurized milk (Perko, 2011). Pseudomonas species are the main psychrotrophic bacteria isolated from refrigerated raw milk, being among the major spoilage agents in the dairy industry (Paula Ana et al. 2011). Presence of the genus Pseudomonas indicates improper cooling and refrigeration of camel milk.