Investigation of Microorganisms Associated with the Spoilage of Onions around Dutsinma Metropolis

Total or since ancient times, onions (Allium cepa, L.) have been an important dietary resource and have also been of interest for medical purposes [1]. Traditionally, onions and plants belonging to the Allium genus have been used as an herbal remedy for a wide range of ailments, due to their association with many pharmacological effects [2,3]. Biological effects attributed to onions have been commonly ascribed to the volatile sulfurcontaining compounds, such as thiosulfinates, mainly responsible for the characteristic taste, aroma and lachrymatory effects [4]. These compounds are formed from cysteine sulfoxide precursors and the effect of the enzyme alliinase which is released from cell vacuoles when tissues are damaged [5]. However, these volatile products are highly unstable and recently, attention has been focused on the effects of phenolic compounds, such as flavonoids, which are more stable [6]. Onion is known for being a good natural source of flavonoids mainly represented by the flavonols quercetin and kaempferol, which are present as their glycosides [7]. Protection of food from pathogens and spoilage organisms has been traditionally achieved by chemical methods, but during recent years there has been an increase in consumer interest in developing Onion which contain a low level or are free of chemical preservatives [8]. The emergence of pathogens which are resistant to classical preservatives has also created an urgent necessity to find alternative antimicrobial agents [9]. In consequence, the food industry is interested in developing natural components for the partial replacement of synthetic antimicrobials [10]. Onions can be considered as a good source of natural additives to retard food deterioration [11]. Numerous benefits have been attributed to onions including prevention of cancer and cardiovascular disorders, reduction in the blood levels of cholesterol, reduction in osteoporosis [12]. Reduction in stomach ulcers, inhibition of the proliferation of cultured ovarian, breast and colon cancer cells, inhibition of platelets-mediated thrombosis, prevention of inflammatory processes associated with asthma, treatment of fever, common cold, cough, sore throat and its use as an antimicrobial agent [13]. Onions are packed locally in baskets and jute bags. These packaging materials come from palm, bamboo and fibrous jute trees. However these materials provide no barriers of dust, and can easily be crushed which might lead to damage of the onions. During storage, some losses occur due to sprouting, drying and rotting [14]. Bulb rots are a common cause of onion loss during storage. They are caused by microorganisms particularly fungi. The black mould disease caused by Aspergillus niger is a limiting factor in onion production worldwide [15]. Aspergillus niger has been reported to survive between onion crops as a soil saprophyte in or on bulbs in field or storage and is ubiquitous in nature. The fungus invades bulbs of onions in field or storage whenever they find injured tissues by producing various enzymes or toxins [16]. Association of Aspergillus niger with onion seeds produced in hot climates and their transmission from soil and naturally-contaminated seeds to onion seedlings cause 30-80% loss or spoilage of onion bulbs [17].