Fungal Infection and Aflatoxin Contaminationon Dried-Stored Spices

A review regarding fungal infection and aflatoxin contamination by Aspergillus flavus during pre and post-tharvest handling on spices is presented. The results of research on spice storage management, physical and chemical treatments on dried spices before storage to prevent fungal infection are discussed


Introduction
Spices have been defined as aromatic natural compounds originated from dried plants or parts of plants such as seeds, fruits, flowers, roots, bulbs, leaves bark used in small quantities and added to preserve food, give taste, smell and flavor (Codex, 2017). Some spices such as ginger, turmeric, galangal, chili pepper, red onion and garlic used in fresh condition or stored several times after harvest. However, dried spices such as white and black pepper, star anise, candle nut, coriander, cardamom, nutmeg, cloves, etc. are processed very complex. Pre-harvest and postharvest handling of the spices such as harvesting, drying and storing can span long periods of time before used (Codex, 1995). As with many agricultural products spices are susceptible infected by microbes. Among microbes, xerophilic storage fungi are the predominant contaminant of dried-stored spices (Kneifel and Berger, 1994 (Dimić et al, 2008) Aflatoxins are mycotoxin produced as secondary metabolite by some strains of Aspergillus section Flavi that grow on improperly stored commodities. Among Aspergillus section Flavi, Aspergillus flavus is one of the aflatoxin producers that distribute world-wide especially in tropical regions (Tran-Dinh et al, 2009). Aspergillus flavus has no specific host and infect a wide variety of agricultural products including spices in the field, during storage, processing and distribution (Leger et al, 2000). However, not all A. flavus strains are toxigenic (aflatoxin producer) (Ehrlich, 2014)  strains have yet to be investigated.
Modified atmosphere packaging on spices have been used only for dried spices. Most filamentous fungi are obligate aerob. Magan et al (1984) and Taniwaki et al (2001) found that to inhibit microbial growth during storage, oxygen level must be lower than 0.14% and carbondioxide level should more than 50%.
Ionizing radiation is another physical treatment to decontaminate microbes of food and feedstuffs. Spices are the most commonly preserved by gamma irradiation where the packaged spices is exposed by gamma photon emitted by Cobalt-60 ( 60 Co) or infrequently Cesium 137 ( 137 Cs) to kill insects and to eliminate microbes. Gamma irradiation dose is different for each kinds of food and feedstuffs. The maximum dose for dry food including spices up to 10 kGy has been considered safe and effective (Farkas, 1998).. Irradiation with maximum dose 10 kGy not radioactive on spice (FAO/IAEA/WHO,1981; Farkas and Mohácsi-Farkas, 2011). and every species of molds has different sensitivity and resistance on gamma irradiation as shown in Table   1. The effectivity of irradiation depend on irradiation dose, moisture content (Aquino, 2012) fungal population (Calado, 2014), melanin pigment (Dadachova and Casadevall, 2008) and the presence of oxygen during irradiation. Fungal with multicell spores such as Alternaria and Fusarium more resistant to irradiation than that of a single spore. Fungal mycelia or spores with pigment (melanin) are less sensitive to irradiation than non-pigmented fungi was reported by Dadachova and Casadevall (2008). Reducing initial microbes and fungal infection by properly pre and posthandling are prerequisite before irradiation is conducted.

Chemical treatmens
The use fumigant on spices such as methyl bromide (CH3Br) and ethylene oxide (EtO) is effective to eliminate molds. however, both of the chemicals are highly toxic compounds, carcinogen when inhaled and has been prohibited in many countries such as Japan and European countries because of the residues it leaves in spices (Chmielewski and Migdal, 2005). In addition, methyl bromide is capable depleting atmosphere ozone layer. The effect of phosphine (PH3), fumigant, used as a treatment to replace methyl bromide for insect control also inhibit A.
flavus and aflatoxin production (Dharmaputra et al, 1991), they reported that phosphine concentration 0.5 mg/L commenced inhibit mycelial growth of the A. flavus.

Conclussion
Pre-harvest and post-harvest handling management of spices are essential particularly in tropical countries where spices were cultivated, dried and stored conventionally. Fungal population in spice distribution chain is determined by farmer level as primary producers. Integrated spice management at farmers level, collectors, distributors and retailers is necessary to minimize fungal infection on each level. Physical treatments by keep dried-stored spices at low water activities during storage and ionizing irradiation (gamma irradiation) are effective to reduce population of storage fungi and aflatoxin contamination.