A review on microbial degradation of drinks and infectious diseases: A perspective of human well-being and capabilities

2.1 Spoilage of soft drinks by yeast

Yeasts are considered to be a common contaminant in soft drinks. It will generally be found in constitutes, raw materials, or the beverage processing environment. Yeasts have an excellent ability to tolerate the range of carbonation beyond 3.0 vol; thus, it is considered to be an essential beverage spoilage microbe. Yeast could also endure acidic conditions; it has a wide range of pH requirements for its growth from 1.5 to 8.5 (Sperber, 2009) with optimum growth conditions between 3.0 and 6.5 (Lawlor et al., 2009). The production of ascospores from yeasts is the primary cause of spoilage in soft drinks prepared thermally. According to the spoilage capability, the yeast is classified into four groups (Table 3). The first group is the additive resistant and the fermentative microbe, which are the primary trouble makers in all the production process steps. The presence of extremophiles are scarce in the production environment, and even if it is present, its concentration will be very low or negligible. Most of the spoilage was caused by these type of microbe. Spoilage by this group will be controlled by additive or preservatives (James and Stratford, 2003). The third group's presence is an indication that the sanitation in the production plant is abysmal, but still, this group of microbe will not spoil the end product. The microbe, which is not typically connected or associated with soft drinks, is the fourth group of yeasts. The intermediate caused by fermentation and turbidity leads to the formation of flavorless end product. Occasionally, swelling of the package or even bursting of the box may occur due to the presence of carbon dioxide. The presence of fermentation spoilage yeasts may lead to gas pressure up to 2 to 7 bars, after growing for 14 days in a soft drink that contains glucose (1 M). Yeasts develop themselves in the soft drinks and pave the way for other microbes to grow in the drinks by solubilizing the preservatives of a weak acid in nature. The authorized limit of alcohol will sometimes exceed in the soft drinks, which are spoiled during fermentation metabolism and lead to ethanol formation and cause the ceiling to exceed. Notably, in the fruit juices and lemonades, the primary contaminant will be Saccharomyces cerevisiae (Back 2005), as it produces a massive quantity of carbon dioxide and also extremely fermentative. Some of the Saccharomyces strains will also have the capability to endure sulphates, sorbates and benzoates (Mollapour and Piper, 2008), which can also produce pectinase, results in clearing the products with hazy natureaert.

A new microbe that causes spoilage in soft drinks, beverages and artificially flavored drinks is identified as Candida davenportii, which rarely causes spoilage and falls in group two spoilage microbe. Zygosaccharomyces bailii is highly notorious because of its characteristic features like higher sugar fermentation, better tolerance for salt, high resistance to weak acids (Steels et al., 2002; Martorell et al., 2007) which is commonly found in sauces and concentrates made with fruits. The Z. bailii also oxidatively degrade and catalyze benzoate and sorbate, paving the way for other spoilage microbes to grow better (Mollapour and Piper, 2008). A few viable cells in the package will affect the quality of end products (Van Esch, 1987). Another Zygosaccharomyces species, Z. lentus was identified to be similar in the physiological properties of Z. bailii. Dekkera yeasts, which produce ascospores, are the usual soft drink spoilers, which grows slowly, and it will take many weeks to develop the symptoms of spoilage. This dekkera yeast has the potential to withstand and grow in a severe concentration of carbonation but significantly less tolerance to benzoates and sorbates. This microbe usually is responsible for the formation of condensed sediments and clouds, which also oxidizes sugars into acetic acid. Dekkara yeast also has the characterization of weak fermentation in less concentration of oxygen. Another common microbe present in soft drinks is D. anomala, which is low fastidious for the vitamin requirement compared to D. naardenensis or D. bruxellensis.

2.2 Bacterial spoilage

Among bacteria, acetic acid and lactic acid bacteria are the common microbes that cause spoilage in soft drinks. These are highly potential microbes to endure highly acidic conditions, which is a key factor in growing and developing soft drinks. Leuconostoc mesenteroides and Lactobacillus paracasei are the common beverage spoiling species. Other strains that are commonly present in polluted products are Weissella confuse, Lactobacillus perolens, Lactobacillus plantarum, Lactobacillus buchneri and Lactobacillus brevis. Various other strains also have the potential to spoil the beer products (Hammes and Hertel, 2009). In apple juice, formic acid indicates that the drink is spoiled. Less astringency and carbonation are due to lactic acid bacteria. Sometimes, ropiness has been seen in the end product; the reason behind this is due to the production of glucose or fructose molecule from sucrose.

Gluconobacter and Acetobacter are the important genera which consist of many spoilage acetic acid bacteria. Apart from these two, Asaia and Gluconacetobacter sp. are commonly associated with soft drinks. The genus Asaia consists of eight species discovered in 2000 (Yamada and Yukphan, 2008). The major microbe group present in ethanol and sugar enriched drinks are acetic acid bacteria (Suzuki et al., 2008). The higher concentration of these microbes indicates poor cleanliness maintained in the production processing environment (Raspor and Goranovich, 2008).

Various microbe forms a biofilm on the surfaces (Horsáková et al., 2009). An important feature of acetic acid bacteria is its acid-tolerant capacity, which tends to grow at a very low pH like 3.6 to 3.8 and sometimes even at 3.0 pH (Suzuki et al., 2008). The ideal temperature for the multiplication of this microbe is from 25 to 30 °C, and its growth and developments in soft drinks may lead to swelling in the package, changes in the flavours, sediment, haze and ropiness formation. Acetic acid bacteria are not as regular contaminants as lactic acid bacteria in soft drinks because of their strict oxygen requirement for its growth. The evolving strain Asaia spp, spoils packed water with fruit flavours and ice tea.

Propionibacterium cyclohexanicum was identified from sour orange juice, which had no flavour, yet this microbe has the potential to grow in psychrophilic conditions in other fruit juices. Optimum temperature and pH for this microbe's growth ranges between 20 and 40 °C and 3.6, respectively. Potassium sorbate and natrium benzoate at a higher concentration, such as 500 mg/l and 1000 mg/l will resist the microbe's growth in juices (Walker and Phillips, 2008). P.cyclohexanicum is thermophilic and could withstand up to 95 °C for 10 min; thus, it can’t be removed in normal pasteurization methods (Walker and Phillips, 2007). Bacillus and Clostridium genus are spore formers, usually not grown in low pH, but the spores will be active in the products. These species will found to spoil the juices from vegetables (pH > 4) when compared to juices made from fruits. The beverage spoiler’s concentration is identified to increase in mixed beverages made from fruit or vegetable juices with cereal fibers. Especially, Clostridium species such as Clostridium sporogenous and Clostridium butyricum causes sour flavour in the end product by spoiling the sugar syrup either during the manufacturing stage or during storage, Since this is highly acid-tolerant and can grow in pH between 3.6 and 3.8 (Hawthorne et al., 1991).

Another important genus in spoiling the fruit juices is Alicyclobacillus is found to spoil the ice tea, lemonade, isotonic water, and fruit juices, which are carbonated and has a wide range of temperature optimum for its growth from 20 to 70 °C which also has the potential to grow in the restricted supply of oxygen supply (Smit et al., 2011). The visual identification of spoilage will be discoloration, haze and sediment formation will be seen in the juices, but it will be difficult to identify. Streptomyces griseus is also a major contaminant in apple juices (pasteurized) which produces earthy and musty flavour, which is a gram-positive and spore producers, which is highly resistant to increased temperatures (Siegmund and Pöllinger-Zierler, 2007).

2.3 Fungal spoilage

The fungus can contaminant the end product, by-product, or raw materials either with mycelium or spores (Filtenborg et al., 2004). The major source of fungal contaminants will be from soil (Tribst et al., 2009). Some species like Rhizopus and Fusarium will grow at a low oxygen concentration, i.e., about 0.01% v/v. Mycotoxin production can be inhibited by increasing the carbon dioxide concentration in media if the oxygen couldn’t be removed. Some of the heat-tolerant microbes belong to the genus of Talaromyces, Neosartorya and Byssochlamys are the major contaminants in products made from heat processes such as purees and juices from fruits and canned fruits (Hocking and Pitt, 2001). Millions of dollars will be lost if the fungus contaminates the beverage industry, especially by Eupenicillium brefeldianum, Neosartorya fischeri, Talaromyces flavus and Byssochlamys nivea (Scholte et al., 2004). Another important microbes group responsible for the spoiling beverage industry is Cladosporium and Penicillium genus (Wareing and Davenport, 2005). Inducers of gushing will be seen if the raw material is highly contaminated by fungus (Table 4). An impulsive over foaming of the beer immediately after the opening of the packed beer is known as gushing. It is considered to be a problematic phenomenon. This activity might be due to the production of gushing factors by the fungus, which presents either in the cereal of malt-based raw materials chosen for brewing (Amaha and Kitabatake, 1981; Munar and Sebree, 1997; Sarlin et al., 2005). It has been shown that contagious hydrophobins from strains of the genera Trichoderma, Fusarium and Nigrospora are responsible for this beer gushing (Sarlin et al., 2007). Hydrophobins are active fungal proteins that are believed to stabilize the bubbles from carbon dioxide by covering the microbubbles with a layer (Draeger, 1996; Pellaud, 2002).

3.1 Yeast spoilage

Fermentative yeasts are the possible spoilers of alcoholic beverages from brewing due to its fermenting capability of sugars in an acidic and restricted oxygen environment. Most of the spoiling strains are resistant to additives. Ciders made from conventional methods was spoiled mostly by Saccharomycodes ludwigii, as it strongly resists the presence of sulphite at a concentration of 1000 to 1500 mg/l and grows in its presence. It can develop during all the manufacturing processes; however, spoilage usually is seen in packed products and might be contaminated during filling of the bottles. High amounts of volatile acids and esters will be produced by the overgrowth of Kloeckera apiculata. A mousy flavour by the presence of tetrahydropyridines compound was produced by Dekkara or Brettanomyces species and Pichia strains at the maturation stage. For the synthesis of tetrahydropyridines, lysine and ethanol are the precursors. Some of the volatile phenol producing microbe from phenolic acids are S. cerevisiae, Sz. Pombe, D. bruxellensis and Z. bailii, these volatile phenols are very dangerous at higher concentrations (Malfeito-Ferreira et al., 2009). By metabolizing the phenolic compounds, they detoxify and protect their cells from the effects of inhibition. Especially, brewers and wild yeast spoiled most beverage spoiling capability (Hutzler et al., 2008).

3.2 Bacterial spoilage

Alcoholic beverage spoiling bacteria mainly belong to Pediococcus and Lactobacillus strains (Fig. 2). During conventional cider manufacturing, Lactobacillus sp, which is alcohol resistant, will switch off the flavours and reduce alcohol yield (Hammes and Hertel, 2006). Lactobacillus sp. juices mainly spoiled cider of Scandinavian type. Due to the higher production of acetic acid by heterofermentative strains, the end product flavour was destroyed (Jarvis, 2003). Bitterness was seen due to the conversion of glycerol 3-hydroxypropionaldehyde, which can modify the acrolein and blend with polyphenols leads to the formation of bitterness (Sauvageot et al., 2000; Garai-Ibabe et al., 2008). Diacetyl will be produced by some Lactobacilli, which results in buttery flavour (Jarvis, 2003). The tetrahydropyridines from hetero fermenters result in off mousy flavour. The usual spoilage seen in natural cider is the ropiness characteristic (Ibarburu et al., 2010). This polysaccharide is usually made up of glucans, especially from glucose.

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Fig. 2

Summary of bacterial pathways leading to spoilage aroma and flavour compounds of wine (Sponholz, 1993; Bartowsky and Pretorius, 2008).

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The common rope forming strains are Lb. suebicus, Lb. diolivorans and Lb. collinoides. Volatile phenols and off medicinal flavors were formed by most Lactobacilli (Hammond et al., 1999). Another important spoilage microbe is Pediococci, which is uniform round cells commonly found in tetrads (Holzapfel et al., 2006). Pediococci may also induce ropiness by producing volatile phenols (Barthelmebs et al., 2000; Couto et al., 2006). P. parvulus is identified in french cider, which is ropy. Other important strains of Pediococci responsible for ropy are P. claussenii and P. damnosus and (Dobson et al., 2002). In the brewing industry, two new strains of Pediococci which are tolerant to ethanol were P. ethanolidurans and P. cellicola were identified (Zhang et al., 2005; Zhang and Dong, 2006) at the highly acidic condition with pH 3.5 (Fig. 3). Two important genera Gluconobacter and Acetobacter could affect the beverage at any time with oxygen availability (Bartowsky and Henschke, 2008). Normal contaminants present in the conventional cider brewing industry are G. oxydans and A. pasteurianus (Jarvis, 2003). Acetic acid bacteria did ethanol oxidization and this will further catabolize the acetic acid into water and carbon dioxide (Bartwosky and Henschke 2008). The product, which is spoiled by this microbe, results in vinegar flavour with ethanol with reduced pH (Raspor and Goranovich, 2008), which will also cause cider sickness. Another microbe responsible for casing cider sickness is Zymomonas mobilis (Coton et al., 2006), a gram-negative anaerobe tolerates a little bit of oxygen produced carbon dioxide and ethanol fermenting glucose and fructose.

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Fig. 3

Minimum requirement of pH for the growth of pathogenic microbe in beverages.

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3.3 Microbiological health risks linked with beverages

Soft drinks are generally considered safe, which will not create any food-borne illness, but that can’t be completely kept out. Around 32 outbreaks had been documented since 1922, with respect to food-borne diseases, mainly by consuming partially sterilized fruit juices. These outbreaks will be mostly by the low production process and cleanliness in the production plant (Vojdani et al., 2008). These outbreaks from beverages were mainly caused by an enteric group of pathogens, including protozoans, viruses and bacteria. But in most of the cases, the identification of the causative agent will be challenging and impossible (Parish, 2009). Another important risk for health with these beverages is mycotoxin from fungus (McCallum et al., 2002).

4.1 Presence of viruses and parasites

Viruses and Parasites were also associated with the outbreaks of disease after fruit juice consumption. Mainly, protozoa will survive only in the host at a resting stage like oocyst, which will be secreted by the hosts already infected by faeces (Dawson, 2005). Through the faecal oral route, the contamination will spread in beverages and food. Some of the oocysts may even cause gastroenteritis (Erickson and Ortega, 2006). From 1990s to 2000s, a protozoan Cryptosporidium partum was identified in juices and ciders. The unprocessed or less processed end products was the main reason for the outbreaks. C. partum oocysts have been appeared to lose >85% of its viable cells for about 24 hrs in beverages like beer of pH around 3.81 to 3.85 and a cola drink with a pH of 2.46 at temperatures of 4 and 22 °C (Friedman et al., 1997). Another important protozoan transmitted through fresh products like raspberries is Cyclospora cayatensis. In developed countries, protozoa's food-borne illness is found to be very less. Since viruses need living cells for its replication, it don't develop in food products. Nonetheless, just a couple of infection particles may bring about a high likelihood of disease. Some viruses like, Hepatitis A, rota, and nota viruses transmit food-borne illnesses by maintaining the worst cleanliness in the production and packaging process. In 1960s, Hepatitis A was found to be transmitted through juices made from orange (Parish, 2009). An outbreak from norovirus was associated with the raspberries cultivated by using contaminated water (Newell et al., 2010).

4.2 Mycotoxins in beverages

The development of filamentous fungi is typically not to be expected in the production of beverages. Nevertheless, during process and storage, various filamentous growths will have the potential to secrete secondary metabolites under stress conditions. When these mycotoxins are absorbed or inhaled or ingested, it will lead to illness or death in humans and animals. Almost in all taxonomy groups, these toxic producing groups and heterogeneous groups will be present (Drusch and Ragab, 2003). Though various mycotoxins are present, only a few possess high food products (Murphy et al., 2006). Usually, the genus of Alternaria, Fusarium, Penicillium, and Aspergillus produces mycotoxins that pose a severe threat to food-borne illness. Fusarium toxins are produced by zearalenone and trichothecenes, while aflatoxin was produced by A. patulin and ochratoxin. A huge amount of mycotoxin may have toxin effects ranging from chronic to acute like immune system suppression and high cancer risk to liver and kidney damages, respectively (Table 5). Mycotoxin will transmit to animals via animal feed and affects its health. This mycotoxin is highly stable and can survive in the entire production process and enter the end product. The major reason for mycotoxin entry in the production process is through the contaminated raw materials like cereal extracts and fruit juices (Boeira et al., 1999). According to the fermentation time, the type of yeast involved, the concentration of toxin the degree of growth will be inhibited (Kelsall and Lyons, 2003).

Another important mycotoxin patulin has drawn considerable attention among researchers because of its spoiling capability of juices from berry and fruits (Delage et al., 2003). Penicillium spp produced this toxin found to contaminate apple ciders, juices from pears and apples. In post-harvest fruits, a blue mould rot disease will be caused by P. expansum. An indirect mutagenic effect like cross-links of DNA to DNA and cell mutation was induced by patulin, which also directly reacts with DNA, which also possess carcinogenic effects. Though the mechanism of the patulin toxicity mechanism was unknown in humans, the U.S. FDA had set 50 ppm is the maximum limit for tolerance in products derived from apple. Other mycotoxins can damage DNA such as penicilpenicillic acid, luteoskyrin, citrinin, zearalenone, sterigmatocystin are a group of aflatoxin (Paterson and Lima, 2010). Various research was done to determine the levels of patulin in cider and apple juice. A study by Harris et al. (2008) found that the patulin concentration in Michigan juices and apple cider to be below the maximum allowed. A report by Murillo-Arbizu et al. (2009) found the patulin to be exceeded in Spain's apple juices. In Northeast China, a survey had been conducted and identified that a higher concentration of patulin of about >50 Pl/l was seen in 16 percentage of apple products like concentrates from apple, baby food, the juice from apple and mixed juices, Youngsters are frequent consumers of apple beverages, and reduce the value from 50 Pg/l in order to protect them (Tangni et al., 2003).

6.1 pH and acidity

pH and acidity are important factors that hinder the beverage quality (Mentz et al., 2010). Usually, the growth of the spoiling microbe will increase with an increase in pH. Naturally, the pathogens that cause food-borne illness will not grow at pH 4.6 (Lawlor et al., 2009). Hence the pH of the alcoholic beverage has to be set below this level. Low pH alone does not guarantee the stability and safety of the end product. The inactivation rate and the minimum pH requirement will be based on the acidulant nature inhibitor presence and the mechanism of resistance for the acids by microbe (Lücke, 2003). The microbe survival was highly affected by weak acids, as these weak acids will strongly inhibit the growth of the microbe in its undissociated forms at low pH conditions. Clostridium sps that produce butyric acids will have optimum growth conditions at the range of pH from 4.0 to 4.5 and at elevated temperatures (Lücke, 2003). Microbes that grow in sweet wort unhoped, Salmonella typhimurium and E. coli H157:07 at a pH of 4.5 and no growth and development were seen at pH 4.5 (Mentz et al., 2010). Some fruit juices with low acid values like watermelon, papaya, persimmon, melon, cantaloupe, and acai contain pathogen of beverage associated. Even though some foods highly acidic inhibit the multiplication of microbe but it couldn’t affect its survival. Hence the pathogenic microbe will survive for longer periods in these juices. The adaptation for acidic conditions will enhance microbe's adaptive capability to preservatives. Protozoans inactivation at lower pH has led to varied results. Most of the viruses associated with food-borne illness are highly acidic tolerant and can survive during fermentation of acidification as a method for preserving the food (Baert et al., 2009).

6.2 Carbonation and oxygen

Soft drinks that are carbonated are less susceptible to spoilage by microbe than soft drinks that are not carbonated. The spoiling microbe's inhibition will be done by lowering the cytoplasmic membrane's pH, sporulation induction, buffering of cytoplasmic perturbation, utilization of amino acid inhibition, cell division inhibition. The average level of carbonation will be around 3 volumes in soft drinks. However, some yeasts have potentially resisted the carbonation in the soft drinks at standard volumes, for example, Saccharomyces and Dekkera genus (Stratford, 2006). Some drinks will be less carbonated than conventional drinks, which will pave the way for spoilage microbe's growth. At a high concentration of CO₂, some viruses will have the potential to survive in a modified atmosphere.

6.3 Nutritional status

The type of microbial spoiling and its rate depended highly on the composition of nutrients used in the brewing industry. Generally, the beverage production ingredients will provide nutrient supplements for the microbial growth that will lead to spoilage (Table. 7). Different beverages possess different nutritional qualities. The high juice containing fortified drinks will represent the rich environment while soft drinks manufactured synthetically represent a poor microbial growth environment. The nutrient less soft drinks will be spoiled by Dekkara species, which is highly tolerant of citric acid. Yeast's spoilage will be enhanced if additional sugar was added to the low sugar formulations as it will improve the susceptible of the juices to the yeast spoilage. Simultaneously, reducing the sugar concentration in rich sugar containing formulations will not reduce the spoilage by the yeast, which is fermentative. Soft drinks with 5 to 10% sugar concentration will also equally get spoiled. A test with an herbal drink without sugar was conducted and found that this drink supported around 150 species of yeast growth, but none can grow in the drink (Stratford, 2006).