Rajko Vidrih

Peach fruit ripening and quality in relation to picking time, and hypoxic and high CO2 short-term postharvest treatments

Peach fruits (Prunus persica L. Batsch, cv Springcrest) were harvested at two ripening stages (flesh firmness of 60 N, first harvest, and 45 N, second harvest) and maintained at 20°C in air (control) or for 24 and 48 h in streams of ultra low (<1%) oxygen (ULO) or high (30%) CO2 concentration and then transferred to air for up to 8 days. The decline in flesh firmness was strongly reduced by ULO and CO2 treatments in fruits of both harvests, although the effect was stronger in fruits picked earlier in which ethylene biosynthesis remained at the basal level. In fruits of the second harvest, endo β-1,4-glucanase (EGase) activity was lower in ULO- and CO2-treated fruits than in control fruits at the end of the 24 h treatment and the following two days in air. Acetaldehyde (AA) gradually accumulated in control fruit and the highest concentrations were detected during late ripening. Both treatments induced a strong accumulation of AA but, with the exception of the 24 and 48 h CO2 treatments performed on fruits of the second harvest, a decrease in AA content was observed when the fruits were transferred to air. A slight increase in ethanol (EtOH) was found throughout the ripening process in control fruits; ULO and CO2 strongly stimulated EtOH production. When fruits were transferred to air, EtOH concentration declined rapidly. Alcohol dehydrogenase (ADH) activity significantly increased in control fruit only in the late stages of ripening. Greater ADH activity was found throughout the experimental period in fruits of the first harvest treated for 24 h in ULO and CO2, whereas, at day 8, control and treated fruits of the second harvest showed similar ADH activity values. Hypoxic and, to a lesser extent, CO2-enriched atmospheres stimulated Adh gene expression.

Cell wall hydrolases and amylase in kiwifruit softening

Abstract The activities of amylase, β-galactosidase (β-GAL), polygalacturonase (PG), and endo-1,4-β-glucanase (EG), and ethylene evolution, were measured during ripening in kiwifruit ( Actinidia deliciosa (A.Chev.) (C.F. Liang et A.R. Ferguson var deliciosa, cv. Hayward). Fruit, harvested at firmness values (FV) of 65 N and a soluble solid (SS) content of 9%, were maintained in air at 20 °C for 40 days, until they reached the edible stage. Fruit firmness decreased throughout the experimental period and the lowest FV (about 5 N) was reached after 38 days of storage. SS content increased rapidly to about 13% within 15 days, then the rate of accumulation slowed and the SS content of 14.1% was reached after 33 days. Ethylene climacteric was a late event occurring at a FV of 10 N. The highest amylase activity was measured at harvest. During storage it declined, although a slight rise was detected at 33 days. β-GAL activity was very low at the beginning of storage and increased throughout the experimental period, while PG activity was detected only after the fruit FV was below 10 N. EG activity decreased within the first three days of storage, then increased and peaked 15 days after harvest. Later, EG activity remained low but increased again at the end of the storage period. Application of propylene (500 ppm) to fruit that had softened to 30 N in air stimulated fruit softening and EG activity, and induced the accumulation of an EG-related peptide: the other enzymes appeared not to be affected by the gas.

Volatile compounds of freeze-dried sour cherry puree affected by the addition of sugars

ABSTRACT The aim of this work was to determine the influence of the addition (5, 10, or 20 g/100 g) of different sugars (sucrose, maltose, or trehalose) prior to freeze-drying on the key volatile compounds of the sour cherry puree. The key volatile compounds of sour cherries were benzaldehyde, benzyl alcohol, and 2-hexenal. The results obtained for the samples with the addition of sugars were compared to the control sample, the sample without sugar addition. The control sample contained 3.92 mg/kg of benzyl alcohol, 856.61 µg/kg of benzaldehyde, and 15.58 µg/kg of 2-hexenal. Benzaldehyde, the compound described as the typical cherry volatile compound, was determined in the highest amount in the sample with the addition of 10 g/100 g of trehalose (937.51 µg/kg). The highest amount of 2-hexenal was determined in samples with the addition of 10 or 20 g/100 g of trehalose (17.45 and 18.96 µg/kg, respectively). All samples with the sugar addition had lower content of the benzyl alcohol than the control sample. Generally, samples with the addition of sucrose had the lowest amount of examined volatile compounds.

Volatile profile of sour cherry puree as affected by sucrose and trehalose

ABSTRACT In this study, effect of sugars (sucrose and trehalose) and their amount on the volatile profile of sour cherry puree was evaluated. Results were compared to sour cherry puree without addition of sugars. Volatiles amount depended on type and amount of sugar. This indicated that the sugars showed an effect on flavour profile. Volatiles with the ethereal, alcoholic flavour note were present in the highest amount in the puree while with the addition of sugars, amount of those volatiles was lower. Sweet, floral volatiles were determined in higher amount when sugars were added in comparison to puree. Addition of sucrose did not have significant impact on the volatiles with sweet flavour note, while with addition of trehalose lower amount of those compounds were determined than in puree. Sweet, fruity and fresh, green volatiles were determined in higher amount in samples with the addition of sugars, especially when trehalose was added. Addition of sugar did not have impact on pungent volatiles.