An immunoaffinity column/HPLC procedure was developed to quantify low levels of ochratoxin A (OTA) in green coffee beans, roasted coffee beans, and soluble (instant) coffee with greater than 80% recoveries. The method was used to survey 116 soluble coffee samples from various countries and different manufacturers and showed contamination levels ranging from “not detectable” to 15.9 μg/kg. The highest levels of OTA were detected among soluble coffees that had been adulterated with coffee husks and/or coffee parchments (mean contamination level:  5.9 μg/kg). By comparison, OTA concentrations in pure soluble coffee samples were significantly lower, with a mean contamination level of 1.1 μg/kg. Although higher than normal figures have been found in some products purchased in East European countries, the results of this survey indicate that pure soluble coffee is not a major source of OTA in the diet, with estimated intakes being well within safety limits. Keywords: Ochratoxin A; soluble coffee; analysis; HPLC; adulteration

As considerable inconsistencies are found in the literature regarding the influence of roasting and subsequent operations on the ochratoxin A (OTA) content of green coffee, experiments were undertaken to assess the evolution of OTA along an industrial soluble coffee manufacturing line. Both the variability and the amount of OTA naturally present in a lot of Thai Robusta green coffee were drastically reduced during soluble coffee manufacture. A small proportion of OTA was eliminated during green coffee cleaning, but the most significant reduction took place during roasting. The roast and ground coffee contained only 16% of the OTA originally present in the green coffee. Two phenomena are responsible for the elimination of OTA during roasting: a thermal degradation and a removal with chaff. Thermal degradation is the most important route of elimination, with <20% accounted for by the chaff. A further 20% reduction was observed during soluble coffee manufacture, so that the powder contained only 13% of the OTA initially present in the green beans.

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Green Robusta coffee was stored in silos for 8 months under industrial conditions in Thailand, and subjected to air-conditioning, aeration, and nonaeration, and compared to bag storage under ambient conditions. Air-conditioning clearly reduced the relative humidity (RH) of the silo atmosphere and the moisture content (MC) and the water activity (a w) of green coffee. Overall storage behavior was better for coffee in the aerated silo (RH = 68%; MC = 13.0%; a w = 0.69) than for coffee stored in bags (RH = 81%; MC = 13.5%; a w = 0.72). Aeration provided an efficient means to reduce MC and a w during the rainy period. Glucose content was linked positively with the increase of a woody/rubbery note in coffee cup quality and increased by ∼50% between months 3 and 6 when green coffee MC and a w increased the most. Glucose is a potential green coffee quality marker. Under the tested storage conditions, neither the growth and presence of ochratoxin A (OTA)-producing fungi nor consistent OTA production was found. OTA contamination appeared to have occurred before storage. Keywords: Coffee; storage; silo; glucose; mold; ochratoxin A