Cold sterilisation of walnuts as potential component of bakery products

Microbiological quality, sensory and chemical changes in volatile and lipid fractions of gamma-irradiated walnuts (Juglans regia L.) were evaluated using gas chromatography/mass spectrometry (GC/MS), gas chromatography with flame-ionising detector (GC/FID) and sensory evaluation. Doses of gamma-radiation were with in the range 0.5 - 5 kGy, where 10 kGy represented the highest permitted dose for food applications. Microbiological analysis showed that gamma-irradiation was an effective sterilisation tool which eliminated prevalent microorganisms including coliform bacteria from initial count of 6.0 x 102 CFU/g with 1.5 kGy dose. The dose of only 0.5 kGy was found to be sufficiently effective for killing prevalent moulds. Quoted levels of ionising radiation were adequate for elimination of microbiological load for minimum storage duration of 2 kGy dose. Higher irradiation levels negatively affected organoleptic properties of studied walnuts. Significant changes in relative contents of certain fatty acids, mainly linoleic and linolenic acid, and closely related changes in relative contents of certain volatiles were observed due to the influence of ionising radiation. Unsaturated hydrocarbons as determined by GC/MS method are believed to be suitable markers of gamma-irradiation of walnuts even at 0.5 kGy dose of application.