Influence of thermal treatment on the stability of phenolic compounds and the microbiological quality of sucrose solution following osmotic dehydration of highbush blueberry fruits.

BACKGROUND: Osmotic dehydration is a process of the partial removal of water which is based on immersion of material having cellular structure in a hypertonic solution. Osmotic dehydration is used as a pretreatment for the dehydration of foods before they are subjected to further processing such as freezing, freeze drying, vacuum drying. Management of spent syrup is one of the most important problems related to osmotic dewatering. Osmotic solutions are heavily polluted with of carbohydrates, remains of the dehydrated material and microorganisms. The aim of this study was to determine the effect of thermal treatment on the content of phenolic compounds and the microbiological quality of sucrose solution used in 15 cycles of osmotic dehydration of highbush blueberry (Vaccinium corymbosum L.) fruits. MATERIAL AND METHODS: The tested material was 65.0 ±0.5°Brix sucrose solution used for 15 cycles of osmotic dehydration of highbush blueberry (Vaccinium corymbosum L.). Osmotic dehydration was conducted at 40°C for 120 min using fruits previously subjected to enzymatic pretreatment. The thermal treatment of sucrose solution was conducted at 70, 80, 90, 100 and 115°C for 20, 40 and 60 s. The sucrose solution was analysed in terms of total polyphenols, particular polyphenols using high performance liquid chromatography and microbiological analysis was subjected. RESULTS: Thermal treatment at 70-115°C for 20 s caused degradation of 8.5% to 12.7% of polyphenols, while as much as 23.1% of polyphenols were degraded at 115°C after 60 s. The present paper proposes heating parameters that are optimal from the point of view of phenolic compound retention and microbiological quality: thermal treatment of syrup at 100°C for 40 s. Under these conditions, total polyphenols retention was 94.5%, while the retention of individual phenolic compounds varied from 89.2% to 37.2%, and that of flavan-3-ols amounted to 89.5%. The studied manner of syrup treatment eliminated the problem of syrup contamination with yeasts and molds (reducing their levels to less than 1 CFU/mL).

Osmotic Concentration of Gooseberry Fruits - The Influence of Temperature, Time and Pretreatment Methods on Mass Transfer and Total Polyphenol and Organic Acid Content.

The objective of the study is to assess the influence of temperature, time and enzymatic pretreatment on the osmotic concentration of gooseberry fruits (cultivar Bialy Triumf). The fruits were osmotically concentrated in a sucrose solution at 65 °Brix and 40 to 70 °C for 5 to 240 min. Two experimental procedures were employed. In the first procedure, prior to concentration the fruits were immersed in the solution containing lipolytic enzymes, and then in the solution containing pectinolytic enzymes. In the second procedure, pectinolytic enzymes were added to the sucrose solution. The kinetics of the osmotic concentration was studied based on the changes in dry matter content, water loss, and solid gain. Higher temperature and longer process time led to higher values of the mentioned parameters. After 1 h of concentration at 40 °C, dry matter content was 13.9%, while at 70 °C it was 20.4%. The use of pectinolytic enzymes during osmotic concentration resulted in higher effectiveness of the process. After 2 h of concentration with the use of pectinolytic enzymes, solid gain was seven times higher than that in the control sample. Enzymatic treatment with lipase and pectinase before concentration also increased solid gain during osmotic concentration (up to twelve times after 2 h at 40 °C). The lower processing temperature, the higher retention of phenolic compounds in fruits was observed. The retention of phenolics was the highest at 40 °C (92.2% at 2 h). Among organic acids (malic, shikimic and citric), the highest retention was exhibited by citric acid; at 1 h of concentration, its fraction in the obtained fruit syrup content was from 95.9 to 83.1% as compared to the starting material.