Involvement of fatty acids in the response to high CO2 and low temperature in harvested strawberries

Fatty acids (FAs) play important roles in membrane fluidity, energy status and the production of specific FA-dependent esters. However, little is known about the modifications in FAs induced by high CO2 that can improve fruit quality and prevent the disorders associated with storage at low temperature. For this purpose, total, free and esterified FAs in neutral and polar lipid fractions were characterized and quantified and their relationship with straight-chain esters was examined in strawberries treated with high doses of CO2 and different times of exposure during early storage at 0 °C. In strawberries stored without added CO2 (T1), storage at 0 °C led to an imbalance in the saturated/unsaturated ratio of polar lipids, mainly due to the decrease in the amount of saturated fatty acids (SFA). In addition, a decrease in the amount of free polyunsaturated fatty acids (PUFA) linked to a prevalence of butanoates and hexanoates esterified to long alcohols was observed. A strong negative correlation (P ≤ 0.01; r ≥ 0.7) between butanoate esters and free PUFA was quantified. In contrast, the application of 2 d 20 kPa CO2 treatment (T2), increased the amount of PUFA from the neutral and polar fractions, with a preference for α-linolenic acid (18:3n3) which results in a rise in the 18:3/18:2 ratio, and which can confer membrane stability and fluidity. Furthermore, our results also showed a strong positive correlation (P ≤ 0.01; r ≥ 0.75) between α-linolenic acid (18:3n3) of polar lipids and some ethyl esters that contribute mostly to the aroma in strawberries. However, 3 d 40 kPa CO2 treatment (T4) depleted the content of FAs from all the lipid fractions in association with deficit ATP levels and an increased lipid peroxidation. These results suggest an active lipid breakdown which could play a causal role in the reported increased leakage of cellular water into intercellular air spaces in stressed-CO2 fruit. Taken together, our results provide new insights into the beneficial effect of 2 d 20 kPa CO2 treatment at 0 °C on the enhancement of PUFA in the polar lipid fraction and on the emission of esters other than ethyl acetate, which could improve membrane fluidity and could contribute to enriching aroma in strawberries.
This work was financed by Spanish Project AGL2017-85291-R (MINECO/AEI/FEDER, UE).