Combined Pulsed Vacuum Osmotic Dehydration and Convective Air-Drying Process of Jambolan Fruits

Jambolan (Syzygium cumini) is a native fruit from Asia that has adapted well to the tropical climate of the Amazonian region. However, due to its limited annual availability and high perishability, the jambolan fruit is still underexploited. Thus, this study aimed to preserve the jambolan through a combined process of pulsed vacuum osmotic dehydration (PVOD) and convective air-drying and to monitor the total phenolic contents (TPCs) and total monomeric anthocyanins (TMAs) during these processes. To this end, jambolan fruits were pretreated with increasing PVOD times. After monitoring of moisture loss, solid gain, weight reduction, water activity, TPC, and TMA, pretreated (PT) and non-pretreated (NPT) fruits underwent convective air-drying (50-70 °C). The PVOD reduced half of the water present in the fruits; nonetheless, PVOD decreased the TPC and TMA over time. The increase in air-drying temperature shortened the drying time for both NPT and PT jambolan, and PVOD reduced even further the drying time of the fruits. Moreover, the fruits pretreated and dried at 60 °C showed promising results, potentially being a good alternative to extend the fruit's shelf life and make it available throughout the year.

Antagonistic Activity of Lactic Acid Bacteria and Rosa rugosa Thunb. Pseudo-Fruit Extracts against Staphylococcus spp. Strains

Staphylococcus bacteria are ubiquitous microorganisms. They occur in practically all environments. They also show the ability to colonize the skin and mucous membranes of humans and animals. The current trend is to look for new natural factors (e.g., plant extracts rich in polyphenols) limiting the growth of undesirable bacteria in food and cosmetics or use as an adjunct in antibiotic therapy. The aim of this study was to evaluate the effect of extracts from Rosa rugosa Thunb. on the antagonistic properties of selected lactic acid bacteria strains in relation to Staphylococcus spp. isolates. The biological material consisted of seven strains of lactic acid bacteria (LAB) and seven strains of bacteria of the Staphylococcus genus. The anti-staphylococcal properties of the Rosa rugosa Thunb. pomace extracts (the tested extracts were characterized by a high content of polyphenols, namely 8–34 g/100 g DM/dm) were tested using the well method. The conducted research showed that the pomace extracts of the pseudo-fruit (Rosa rugosa Thunb.) had the ability to inhibit the growth of Staphylococcus spp. bacteria. The minimum concentration of polyphenols inhibiting the growth of staphylococci was in the range of 0.156–0.625 mg/mL. The conducted research showed that combined lactic acid bacteria and extracts from the pomace from the pseudo-fruit Rosa rugosa Thunb. (LR systems) may be factors limiting the growth of Staphylococcus spp. bacteria. As a result of the research, two-component antagonist systems consisting of LAB cultures and extracts from Rosa rugosa Thunb. pomace were developed, which effectively limited the growth of the test strains of Staphylococcus spp. In 41% of all tested cases, the zone of inhibition of growth of bacteria of the genus Staphylococcus spp. after the use of two-component antagonist systems was higher than that as a result of the control culture (without the addition of extracts).

Mass transfer during osmotic dehydration and its effect on anthocyanin retention of microwave vacuum-dried blackberries

BACKGROUND

The combination of sugar osmotic dehydration and microwave vacuum drying is an effective method for the dehydration of blackberries, the retention of their antioxidant properties, and the extension of their shelf life. Mass transfer during the osmotic dehydration of blackberries in sugar solution was investigated together with its influence on microwave vacuum drying characteristics, and the retention rate of anthocyanins in dried frozen blackberries.

RESULTS

The concentrations of the osmotic solutions that were tested contained 40%, 50%, and 60% sugar, and the osmotic solution temperatures were 30 °C, 40 °C, and 50 °C. The solution-to-blackberry mass ratio was 10:1 (w/w) and the process duration varied from 0 to 5 h. A two-parameter mathematical model was used to describe mass transfer in the osmotic dehydration of blackberry samples and estimate moisture loss and solid gain in the final equilibrium. The results showed that the dehydration rate and solid gain rate of the blackberries increased with an increase in osmotic concentration, osmotic time, and the temperature of the solution under certain experimental conditions. The effective diffusivity of moisture and solute were estimated using the analytical solution of Fick's second law of diffusion. The moisture and effective diffusivities of sugar in the above osmotic dehydration conditions were in the range of 1.77 × 10^-9 -2.10 × 10^-9 and 1.36 × 10^-9 -1.60 × 10^-9 m² .s^-1 , respectively.

CONCLUSION

The pretreatment of sugar osmosis greatly reduced the microwave vacuum drying time in the latter part of the dehydration period and increased anthocyanin retention. © 2019 Society of Chemical Industry.