Observations on long-term storage and processing of Jerusalem artichoke tubers ( Helianthus tuberosus)

Abstract

A study was undertaken to determine the effect of the period, temperature of storage and over-wintering in the soil, upon the fructooligosaccharide (FOS) profile of Jerusalem artichoke tubers (JAT). Additional experiments were conducted to determine if changes in FOS profile were related to difficulties in spray-drying macerated tubers for the purpose of producing JAT flour. Tubers from four Jerusalem artichoke cultivars (Columbia, Challenger, Sunroot and Fusil) were harvested, trimmed, washed, placed in (150 μm) polyethylene bags and evaluated for storage stability and changes in fructooligosaccharide (FOS) profile. Of the five storage treatments tested (5°C, 2°C, −10°C, program cooled to −10°C, and ambient) the 2°C treatment yielded the best quality tuber at the end of 12 months of storage. Tubers kept at 5°C showed signs of sprouting after six months and some spoilage after 12 months. The other treatments were unsatisfactory. During short-term storage (18 weeks) the inulin content of the JAT shifted to the shorter chain FOS. Tubers stored for 16 months at 5°C had virtually no FOS with a dp ≥ 10, but had accumulated substantial amounts of dp 1–4. Difficulties in spray-drying a heat-treated macerate of the tubers were not related to the FOS content, but appeared to depend on the degree of hydration of the insoluble fibre components. The colour of JAT flour produced by spray-drying was substantially improved by heating the whole tubers prior to maceration. This serves to inactivate polyphenol oxidase, responsible for the undesirable brown colour development.