SummaryThe levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha -1. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch) -l whereas starch from plants grown with 30 kg P ha -l contained 20.6 nmol P (mg starch) -1. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l -l, respectively. Plants grown with no Pfertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.

Precooked vacuum-packed potatoes are widely used in catering. The influence of different processing temperatures on texture kinetics of water and steam cooked vacuum-packed potatoes was studied. At temperatures above 90C the initial decline in cohesion of steam cooked vacuum-packed potatoes was followed by an increase in cohesion when processed for more than 30 min. Preheating of vacuum-packed potatoes at 70C and 75C increased their cohesion and thereby jirmness.Steam cooked vacuum-packed potatoes processed in multilayer barrier pouches having a low oxygen permeability (0.9 cm3/m2/24h/atm) compared with standard pouches had a more intense and stable yellow surface color, as well as they developed significantly less off-flavor after storage. The oxygen permeability of the pouches had no effect on the content of vitamin C, neither during processing nor after storage. The vitamin C content of steam cooked vacuum-packed potatoes was unaffected by processing time.

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