Ice nucleation in fruit juice from different varieties of sea buckthorn Hippophae rhamnoides L.

(T)he main aim of the investigation was to study the effects of climate on the ice nucleation temperatures of fruit juice from sea buckthorn, Hippophae rhamnoides L. This could provide information on possible adaptive values of ice nucleators in the fruits. It was also an aim to provide information on ice nucleation of fruit juice from different varieties of sea buckthorn. This was done to find suitable varieties for agricultural production of ice nucleator containing fruit juice. Such food grade ice nucleators can be used in the processing of food stuffs particularly where large ice crystals are desired. The ice nucleation temperatures were low in juice from unripe fruits in the summer, and peaked at - 6 degrees C in the autumn. There were no significant differences in nucleation temperatures in juice from fruits grown along a climatic gradient along the Trondheimsfjord. Juice from varieties originating from different parts of the world, but grown at the same fields, showed different mean nucleation temperatures, ranging from - 15.1 degrees C in a Swiss wild type of subsp. fluviatilis to - 6.1 degrees C in a Swedish wild type of subsp. rhamnoides. Varieties with very potent nucleators (- 2 degrees C to - 3 degrees C) were found, but these nucleators were present in low concentrations. Varieties with high concentration of nucleators within a small temperature range (- 6 degrees C to - 7 degrees C) were also found. No correlation between geographic origin and nucleation temperatures was found. Depending on conditions, freezing the fruits had either no, or a negative effect on the germination success. Since no adaptive benefit to the sea buckthorn could be demonstrated, the nucleating ability of the fruit juice is probably incidental.