MAPLE SIRUP. XIV. ULTRAVIOLET IRRADIATION EFFECTS ON THE GROWTH OF SOME BACTERIA AND YEASTS^a

Abstract

Collection of maple sap has undergone drastic changes in the last few years. The conventional spout and bucket system is rapidly being replaced by transparent plastic bags and, more recently, by plastic tubing capable of transporting sap directly from trees to collection tanks.Maple sap is susceptible to microbial infection, which, when it occurs, lowers the quality of the syrup. Recent studies in this laboratory (14,18) have shown that sufficient ultraviolet radiation from sunlight is transmitted through plastic bags and tubing to cause a reduction in microbial populations of naturally-contaminated and inoculated maple sap. The advantages of a collection system which permits entrance of sunlight are apparent. It was considered that the use of germicidal lamps for the disinfection of contaminated sap and for keeping stored sap sterile might have even greater potentials in the control of microbial infection.Since the first observations on the germicidal action of sunlight by Downes and Blunt (12,13), the effects of solar radiation have been reported for a variety of organisms (2,3,22,24,25). It is generally acknowledged that the most lethal portion of the sunlight spectrum is in the vicinity of 260-270 mmc (6,7,9,17). The germicidal effect (4,5,9,20,21) as well as the mutagenic effect (23, 26) of ultraviolet radiation have been reported by several workers.The beneficial effect of mild heating or slightly elevated temperatures during post-irradiation treatment has been observed by several workers (8,11,16). Data are not available, however, comparing recovery rates at low and moderate incubation temperatures.Extensive studies have not been made comparing the effectiveness of a single dosage of radiation with an equal dosage given in several periods of shorter exposure. Coblentz and Fulton (9) found little if any differences in the survival rates of Bacterium. coli corn~~~tnis exposed to radiation continuously or intermittently with short and long intervals of rest.The influence of flow rate of a liquid menstruum during exposure to ultraviolet radyation was investigated by Cortelyou et al (10). As anticipated, decreased destruction rates were observed in faster moving fluids.The purpose of this investigation was to study the effect of ultraviolet radiation on microorganisms in maple sap. The variables tested were chosen from conditions which prevail naturally or which are controllable during sap collection. Representative strains, isolated from naturally-contaminated a Presented at the 19th Annual Meeting