Determination of Chemical Composition of Plums During Pre-Treatment and Drying

Abstract

Thanks to drying, fruits are available on the market throughout the year. Parameters of drying conditions affect eg the content of bioactive compounds in the product. The aim of the study was to investigate the effect of pretreatment conditions and the applied drying method on changes in the chemical composition of plums. Analyses were conducted on plums cv. 'Valor', which were subjected to pre-treatment including blanching, drilling and osmotic dehydration. Next they were dried by the convection method at air temperature of 60°C and flow rate of 1.5 m/s. Dehydration was run in a 61.5% sucrose solution at a temperature of 50°C for 1 or 2 h. Convection-dried plums, with no osmotic dehydration applied, constituted the reference sample. In fresh, dehydrated and dried fruits determinations included dry matter, polyphenols by colorimetry with the Folin reagent and contents of sugars by colorimetry using 3,5-DNS acid. As a result of blanching and dehydration the content of dry matter increased. Water loss after dehydration amounted to as much as 1.45 g H2O/g d.m.0 after 2 h in comparison with blanched plums. As a result of dehydration total contents of sugars and polyphenols in plums decreased (mg/100 g d.m.). In convection-dried prunes the content of polyphenols was by 30÷50% higher than in the raw material, but lower than in the reference sample.Keywords: plums, drying, osmotic dehydration, polyphenols Plums (P. domestica L.) are raw materials relatively rich in polyphenolic compounds, in which respect they exceed eg grapes, strawberries, raspberries and apples [1]. Literature data present plums as fruit of medium or high antioxidant capacity amounting to 10 µmol Trolox/g f.m. or 310 mg AA/100 g f.m., thus making plums rank second or third, after strawberry, in the group of 30 fruit analysed in cited studies [2,3]. Moreover, plums are a valuable source of dietary fiber, minerals, particularly potassium, and beta-carotene [4][5][6]. These characteristics result in the advantageous action, confirmed by numerous studies, of fresh and dried plums on the functioning of the organism, eg an improvement of the blood lipid profile and a reduction of bone mass losses in women [7], improvement of lipid and glucose metabolism [8], and prevention of osteoporosis [9,10]. Plums are valuable dessert and processing raw materials, with prunes being one of the most popular products. They may be an additive for many foodstuffs and dishes, but also with increasing frequency they constitute a high-fiber snack, which may replace sweet, high-energy chocolate bars. Consumers searching for natural food rich in bioactive compounds select prunes, which are associated with being components of cereals or a high-value healthy snack [11]. Drying of fruit makes it possible to ensure their availability on the market throughout the year. Parameters of drying conditions affect eg the content of polyphenols and antioxidant capacity in the product [12]. Osmotic dehydration may be applied as pretreatment before convection drying, facilitating t...

Applicability of Plums Grown in Poland to Drying Process in Terms of Changes in Bioactive Compounds and of Maillard Reaction Products Being Formed

“…Śliwki zawierają średnio od 70 do 90 % wody [41,47]. Średnia zawartość suchej masy wynosi ok. 16 % [21,27,49,50], przy czym najwięcej (20,7 %) oznaczono jej w owocach odmiany 'Węgierka Zwykła'. Zawartość ekstraktu w owocach odmian uprawianych w Stanach Zjednoczonych waha się od 9,9 do 14,3 % [42] i jest mniejsza niż w odmianach krajowych (12,0 ÷ 20,4 %) [48].…”

“…W śliwkach uprawianych w Polsce oznaczono ich 13,5 % ś.m. [50]. Skład cukrów tworzą głównie: glukoza, fruktoza, sacharoza i sorbitol.…”