Effect of electrical field strength applied by PEF processing and storage temperature on the outgrowth of yeasts and moulds naturally present in a fresh fruit smoothie.
Pulsed electrical field (PEF) technology offers an alternative to thermal pasteurisation of high-acid fruit juices, by extending the shelf life of food products, while retaining its fresh taste and nutritional value. Substantial research has been performed on the effect of electrical field strength on the inactivation kinetics of spoilage and pathogenic micro-organisms and on the outgrowth of spoilage micro-organisms during shelf life. However, studies on the effect of electrical field strength on the inactivation and outgrowth of surviving populations during shelf life are missing. In this study, we assessed the influence of electrical field strength applied by PEF processing and storage temperature on the outgrowth of surviving yeast and mould populations naturally present in fresh fruit smoothie in time. Therefore, an apple-strawberry-banana smoothie was treated in a continuous-flow PEF system (130L/h), using similar inlet and outlet conditions (preheating temperature 41°C, maximum temperature 58°C) to assure that the amount of energy across the different conditions was kept constant. Smoothies treated with variable electrical field strengths (13.5, 17.0, 20.0 and 24.0kV/cm) were compared to smoothies without treatment for outgrowth of yeasts and moulds. Outgrowth of yeasts and moulds stored at 4°C and 7°C was analysed by plating and visual observation and yeast growth was modelled using the modified logistic growth model (Zwietering model). Results showed that the intensity of the electrical field strength had an influence on the degree of inactivation of yeast cells, resulting in a faster outgrowth over time at lower electrical field strength. Outgrowth of moulds over time was not affected by the intensity of the electrical field strength used. Application of PEF introduces a trade-off between type of spoilage: in untreated smoothie yeasts lead to spoilage after 8days when stored at 4 or 7°C, whereas in PEF treated smoothie yeasts were (partly) inactivated and provided outgrowth opportunities for moulds, which led to spoilage by moulds after 14days (7°C) or 18days (4°C).
Wageningen UR Food & Biobased Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands. Electronic address: rian.timmermans@wur.nl.
R A H
RA
Timmermans
Wageningen UR Food & Biobased Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands.
A L
AL
Nederhoff
Wageningen UR Food & Biobased Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands.
M N
MN
Nierop Groot
Food Quality & Design Group, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
M A J S
MA
van Boekel
Wageningen UR Food & Biobased Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands.
H C
HC
Mastwijk
D004560:Electricity; D005519:Food Preservation / Q000379:methods*; D031985:Fragaria / Q000382:microbiology*; D005638:Fruit / Q000382:microbiology*; D000067030:Fruit and Vegetable Juices / Q000382:microbiology; D027845:Malus / Q000382:microbiology*; D028521:Musa / Q000382:microbiology*; D061352:Pasteurization / Q000379:methods; D013696:Temperature; D015003:Yeasts / Q000254:growth & development*
Competition; Electrical field strength; Global modeling; Pulsed electric field (PEF); Shelf life; Visual spoilage; Yeast and moulds