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AbstractThe combination of preharvest treatments with calcium chloride and fungicides, and storage of maturity graded fruit were assessed in five European plum cultivars. At harvest, samples of fruit within a commercially suitable range in ripening were divided into two categories: less-ripe (tree ripe-) and more-ripe (tree ripe+). The fruit were stored for 10–14 days at 4 °C followed by 2–3 days at 20 °C before the assessment of fungal decay. If calcium chloride was applied six times each season, postharvest fruit decay was significantly reduced in four of nine experiments, with a total mean reduction of around 50%. Two calcium applications in combination with a fungicide treatment reduced decay by approx. 60% compared to the untreated in one experiment. In six of seven experiments there was no effect of preharvest fungicide applications. In six of 10 experiments, fruit of the category tree ripe- had fewer fruit with fungal decay after storage than the tree ripe+fruit. The higher incidence in the category tree ripe+fruit was primarily due to brown rot, Mucor rot, and blue mould. For the category tree ripe+, there was two to ten times more decay than on tree ripe- fruit after a simulated shelf-life period. To ensure low incidence of fungal decay, fruit of commercial harvest maturity may thus be separated in two ripening categories, one for rapid distribution to the market (tree ripe+) and another for extended distribution time (tree ripe-).

Plums contain high levels of hydroxycinnamates (neo-chlorogenic acid, Neo-CGA), anthocyanins (ATH) and ascorbic acid. The drying process influences their phytochemical content and plum cultivars are known to have different phytochemical retention after drying, but little data exists regarding to possible differences between conventional (CONV) and organic (ORG) plums. The aim of this study was to evaluate the phytochemical content in three different CONV and ORG plum cultivars (Jubileum, Reeves and Victoria) after freeze drying (FD), conventional oven drying (OD) and solar drying (SD). The three cultivars responded differently to the methods of drying. Notably, Jubileum decreased its ATH mostly when subjected to OD while its Neo-CGA content was mostly reduced after SD. Additionally, ORG Victoria and Reeves stood out for the low decrease of Neo-CGA after drying compared to the same cultivars cultivated with conventional system. The Folin-Ciocalteu index, which was significantly different in OD (6942 mg GAE/kg dw) and SD (5420 mg GAE/kg dw) samples, was positively related with both Neo-CGA and hydroxymethylfurfural. The present findings suggest that for some cultivars, the organic system influences the nutraceutical quality of dried product, thus representing an important factor that regulates the phytochemical content of dried plums.

The present work studied the effect of the year of harvest, the genotype and the cultivation method on the nutritional quality and the allergen content of three plum cultivars. The common quality parameters and the phytochemical content strongly varied with the year and the cultivar, while the system of cultivation had a minor influence. In particular, ascorbic acid greatly decreased in 2016 compared to 2015, while polyphenols were higher in 2016. The health-promoting compounds, and particularly phenolics, were significantly correlated with the antioxidant capacity. Finally, the allergen content was strongly dependent on the content of flavan-3-ols, suggesting that this class of phenolics is determinant in influencing the allergen content in plums. Results showed that the major factor affecting the quality and the concentration of natural metabolites of plum, in addition to the diversity among genotypes, is the year-to-year variation, whereas the system of cultivation plays a marginal role.

Knowledge of the respiration rate of a fresh produce is a key factor in the choice of appropriate packaging. Ethylene and CO2-production and O2-consumption were measured for nine Prunus domestica plum cultivars grown on the west coast of Norway. Respiration and ethylene production were measured at 2 °C and 6 °C over two seasons. For three cultivars measurements were made at two or three maturity stages of the plums. Ethylene production ranged from 0.2 to 4.1 and 0.3 to 4.8 ml ethylene/kg−1 h−1 at 2 °C and 6 °C, respectively. CO2-production ranged from 2.6 to 4.8 ml CO2/kg−1 h−1 at 2 °C and from 4.0 to 7.3 CO2/kg−1 h−1 at 6 °C. O2-consumption ranged from 2.5 to 4.8 ml O2/kg−1 h−1 at 2 °C and from 4.4 to 8.0 O2/kg−1 h−1 at 6 °C. On average, ethylene production, CO2-production and O2-consumption rate values were 21%, 54% and 66%, respectively, higher at 6 °C compared to 2 °C, indicating that respiration rate was more sensitive to temperature changes than the ethylene production. Some seasonal differences in respiration rate and ethylene production were measured for some of the plum cultivars. ‘Victoria’ had a typical climacteric fruit pattern, whereas ethylene production of ‘Reeves’ increased with maturity stage, but had an atypical respiration rate. Ethylene production in ‘Jubileum’ was low (0.2 and 0.3 ml ethylene/kg−1 h−1 at 2 °C and 6 °C, respectively) and did not climax. In general, the relatively high postharvest respiration rates of Norwegian plums combined with low sensitivity to high CO2-concentrations imply that commercial micro or macro-perforated packaging materials for plums should have high gas transmission rate.

During the picking season in the Norwegian plum production areas, the harvested plums are brought to cold storage in packing houses once or twice a day. Plums picked late in the afternoon may even not be cooled properly until the next day. The average time from picking until the plums are placed in a cold storage is approximately 8 hours. Previous reports have shown that delayed cooling of sweet cherries and apples reduced the fruits’ susceptibility to physiological or fungal decay. An experiment was performed in order to evaluate the impact of different delay-to-cold storage times (0, 5, 10, 15 and 25 hours) on quality and phenolic contents changes of Norwegian ‘Mallard’ plums during cold storage, transport, and retail in normal atmosphere (NA). The fruits (10 fruits in PE tray, n=3) were stored for 14 days at 1°C, followed by 3 days at 7°C and then for 4 days at 20°C. Fruit quality parameters (firmness, colour in CIE L, a*, b* colour space, weight, rot occurrence (%)) and total phenol and anthocyanin content were determined. Samples were analyzed just before cold storage and then after 14 days at 1°C, 3 days at 7°C, or 4 days at 20°C. Evaluation of results has shown that delay of cooling has a retarding effect on rot development during 20°C storage (post cold transport), weight loss and stimulates anthocyanin accumulation and colour changes to some extent. At the end of storage no effect on fruit firmness could be observed.

Six European plum cultivars ( Prunus domestica L.) grown in Norway have been studied with respect to phenolic composition. Neochlorogenic acid was found to be the most important phenolic acid in all cultivars. Together with other phenolic acids, this compound varied significantly in amount among the cultivars. Cyanidin 3-rutinoside was found to account for60% of the total anthocyanin content. Minor amounts of flavonols (rutin and quercetin 3-glucoside) were detected in all cultivars. Total antioxidant capacity varied from 814 to 290 micromol of Trolox 100 g(-1) of fresh weight. Measurement of total phenolic content in terms of Prussian blue complex formation revealed a method failure of magnitude order compared to results obtained by HPLC. Comparison of the response factors of a range of phenolic compounds obtained upon analysis by the Prussian blue and Folin-Ciocalteu assays revealed that the latter method returned higher yields in terms of gallic acid (GAE).

(1980). Threshold Values of Soluble Solids in Fruit Determined for the Fresh Fruit Market. Acta Agriculturae Scandinavica: Vol. 30, No. 4, pp. 445-448.

The threshold values of soluble solids for acceptable quality are 14.2%, 12.5%, 11.3% and 10.8% in sweet cherries, plums, pears and apples respectively. In plums and apples the soluble solids: titratable acidity ratio is an even better criterion. This ratio should be between 12 and 24 in plums and above 16 in apples. Firmness, as recorded by penetrometer, is a good index of textural quality in apples and pears. The threshold values of acceptable texture are 5.75–2.75 kg in apples and 5–2 kg in pears. Size is closely related to quality in sweet cherries and plums. In apples and pears a yellow ground colour indicates a good eating quality. Surface colour is a reliable criterion in partially blushed apples and in sweet cherries and plums at harvest.

The native ribosomal subunits of the mouse plasmacytoma cell line MPC-11 were fractionated by CsCl gradient centrifugation into seven classes of particles designated p1, p2, p3, p4, p5, p6 and p7, which possessed densities of approximately 1.38, 1.43, 1.46, 1.49, 1.50, 1.51 and 1.53 g/cm3 respectively. The RNA was analysed by oligo(dT)-cellulose chromatography and gel electrophoresis. In both well-fed and starved cells p3 was generally the dominating class of particles. During metabolic shift-up conditions, however, there was a great increase of p6 particles. Transfer of material containing rRNA and mRNA into this region of the CsCl gradient indicates the accumulation of an initiation complex containing mRNA. During metabolic shift-down conditions a decrease of p6 particles and an increase of p2 and p3 particles was observed. The p2 fraction was rich in mRNA and may contain considerable quantities of messenger ribonucleoprotein particles. A substantial fraction of newly synthesised mRNA-containing material in starved cells banded in fact in the p2 region of the CsCl gradients. Circumstantial evidence indicates the existence of a transient 40-S initiation complex which bands in the p2-p3 region of the gradients. Double-labelling experiments demonstrated that radioactivity in 40-S subunits first appeared in precursor particles with a density of 1.49–1.50 g/cm3 and only later in p3 and p6 particles. p7 particles were detected in starved cells. They were slowly labelled and were presumably derived from old ribosomes following completion of the polysome cycle.