ACTA Scientiarum Polonorum - Technologia Alimentaria News en (c) Wydawnictwo Uniwersytetu przyrodniczego w Poznaniu Directions on the use of stevia leaves (Stevia Rebauidana) as an additive in food products

Due to the high intake of sugars, especially sucrose, global trends in food processing have encouraged producers to use sweeteners, particularly synthetic ones, to a wide extent. For several years, increasing attention has been paid in the literature to the stevia (Stevia rebauidana), containing glycosidic diterpenes, for which sweetening properties have been identifi ed. Chemical composition, nutritional value and application of stevia leaves are briefl y summarized and presented.

Modelling of nectarine drying under near infrared – Vacuum conditions

Background. Drying of nectarine slices was performed to determine the thermal and physical properties in order to reduce product deterioration due to chemical reactions, facilitate storage and lower transportation costs. Because nectarine slices are sensitive to heat with long drying period, the selection of a suitable drying approach is a challenging task. Infrared-vacuum drying can be used as an appropriate method for susceptible materials with high moisture content such as nectarine slices.
Material and methods. Modelling of nectarine slices drying was carried out in a thin layer near infraredvacuum conditions. Drying of the samples was implemented at the absolute pressures of 20, 40 and 60 kPa and drying temperatures of 50, 60 and 70°C. Drying behaviour of nectarine slices, as well as the effect of drying conditions on moisture loss trend, drying rate, effective diffusion coeffi cient, activation energy, shrinkage, colour and energy consumption of nectarine slices, dried in near infrared-vacuum dryer are discussed in this study. Six mathematical models were used to predict the moisture ratio of the samples in thin layer drying.
Results. The Midilli model had supremacy in prediction of nectarine slices drying behaviour. The maximum drying rates of the samples were between 0.014–0.047 gwater/gdry material·min. Effective moisture diffusivity of the samples was estimated in the ranges of 2.46·10-10 to 6.48·10-10 m2/s. Activation energy were computed between 31.28 and 35.23 kJ/mol. Minimum shrinkage (48.4%) and total colour difference (15.1) were achieved at temperature of 50°C and absolute pressure of 20 kPa. Energy consumption of the tests was estimated in the ranges of 0.129 to 0.247 kWh.
Conclusion. Effective moisture diffusivity was increased with decrease of vacuum pressure and increase of drying temperature but effect of drying temperature on effective moisture diffusivity of nectarine slices was more than vacuum pressure. Activation energy was decreased with decrease in absolute pressure. Total colour difference and shrinkage of nectarine slices on near infrared-vacuum drying was decreased with decrease of vacuum pressure and decrease of drying temperature.

Changes of antioxidant potential of pasta fortified with parsley (Petroselinum Crispum mill.) leaves in the light of protein-phenolics interactions

Background. Pasta is considered as an effective carrier of prohealth ingredients in food fortifi cation. The aim of this study was to examine the changes of antioxidant potential of wheat pasta affected by fortifi cation with powdered parsley leaves. A special attention was paid to effectiveness of fortifi cation in the light of proteinphenolic interactions.
Material and methods. To improve antioxidant activity of pasta, part of wheat fl our was replaced with powdered parsley leaves from 1% to 4% (w/w). The total phenolics content was determined with Folin-Ciocalteau reagent. Antioxidant capacity was evaluated using in vitro assays – abilities to scavenge free radicals (ABTS) and to reduce iron (III) (FRAP). Predicted phenolic contents and antioxidant activity were calculated. To determine the protein-phenolics interactions SE-HPLC and SDS-PAGE techniques were used.
Results. Fortifi cation of pasta had a positive effect on its phenolic contents and antioxidant properties. The highest phenolics level and antioxidant activity of pasta were obtained by supplementation with 4% of parsley leaves. However, in most cases experimental values were signifi cantly lower than those predicted. The protein profi les obtained after SDS-PAGE differed signifi cantly among control and enriched pasta. Furthermore, the addition of parsley leaves to pasta resulted in increase of peaks areas obtained by SE-HPLC. Results indicate the occurrence of the protein-phenolics interactions in fortifi ed pasta.
Conclusion. Overall, the effectiveness of fortifi cation and consequently biological effect is limited by many factors including interactions between phenolics and pasta proteins. In the light of this results the study of potential interaction of bioactive supplements with food matrix should be taken into account during designing new functional food products.

Eff ects of natural antioxidants on colour stability, lipid oxidation and metmyoglobin reducing activity in raw beef patties

Background. Minced meats undergo oxidative changes and develop rancidity more quickly than intact muscle since grinding exposes more of the muscle surface to air and microbial contamination. Due to concerns about toxicological safety of synthetic antioxidants, recent studies have put more focus on natural antioxidant compounds derived from food components.
Material and methods. The effects of four natural antioxidants (vitamin E, carnosine, grape seed extract and tea catechins) on oxidative processes and metmyoglobin reducing activity in raw beef patties during refrigerated (4°C) storage were investigated and the results were compared with butylated hydroxyanisole treatment patties. The correlation of lipid oxidation, colour and metmyoglobin reducing activity of beef patties were also studied.
Results. Samples treated with carnosine had the highest redness values on the eighth day. Tea catechins, vitamin E and grape seed extract showed higher protective effect against lipid oxidation than carnosine. Metmyoglobin reducing activity increased greatly in all samples during the storage. Signifi cant correlation between redness value and lipid oxidation was demonstrated, while a weak correlation between metmyoglobin reducing activity and any other parameters was shown.

The eff ect of addition of selected vegetables on the microbiological, textural and fl avour profi le properties of yoghurts

Background. Vegetables, apart from having high nutritional value, also contain considerable amounts of dietary fi bre and other components, which may affect physico-chemical properties of fermented milks, e.g. viscosity, texture, susceptibility to syneresis, fl avour profi le etc. The present work was established to study the effect of selected vegetables addition on the rheological, textural, microbiological and fl avour profi le parameters of yoghurts.
Material and methods. The vegetable preparations (carrot, pumpkin, broccoli and red sweet pepper) were added (10% w/w) to the processed cow’s milk fermented with DVS yoghurt culture. Texture profi le analysis, determination of viscosity, susceptibility to syneresis and descriptive fl avour evaluation were conducted at the 1st, 7th and 14th day after production. Additionally, microbiological studies were performed for 28 days, at 7-day intervals.
Results. The highest apparent viscosity and adhesiveness were obtained for the carrot yoghurt, whereas yoghurt with pumpkin was the least susceptible to syneresis. The other texture parameters were not affected by the addition of vegetables. Broccoli and red sweet pepper fl avours were dominating in the fermented milks fortifi ed with these vegetables, whereas carrot and pumpkin fl avours were less distinctive. Yoghurt supplemented with red sweet pepper got the highest sensoric acceptability. The number of starter bacteria was not infl uenced by the vegetable additives, except for pumpkin yoghurt, which contained lower population of lactobacilli.
Conclusions. Among all tested vegetables, carrot additive had the greatest potential to improve yoghurt structure, whereas red sweet pepper imparted the most acceptable fl avour.

Antioxidant activity of polyphenols of adzuki bean (Vigna angularis) germinated in abiotic stress conditions

Background. Adzuki sprouts are one of more valuable but still underappreciated dietary supplements which may be considered as functional food. Sprouting reduces anti-nutritional factors and increases the bioavailability of macro and micronutrients and also affects phytochemical levels. Exposure of plants to abiotic stresses results in change in production of phytochemical compounds. The aim of this study was to assess the content and antioxidant properties of phenolic in adzuki bean seeds germinated in selected abiotic stress conditions.
Material and methods. Adzuki bean seeds were germinated in different abiotic stress conditions: thermal, osmotic and oxidative. The content of phenolics in adzuki bean seeds coat extracts and antioxidant activity Fe2+ chelating ability and neutralization of the free radicals generated from DPPH and ABTS were determined.
Results. All applied stress conditions (except for thermal stress) have caused decrease the content of the analysed phenolic fractions. The lowest amounts of polyphenols in extracts of sprouts obtained in oxidative stress conditions were observed. The highest ability to neutralize free radicals generated with ABTS and DPPH have extracts from sprouts germinated under thermal stress 39.94 and 13.20 μmol TEAC/g d.w., respectively. The lowest – sprouts obtained in oxidative stress conditions (18.2 and 9.72 μmol TEAC/g d.w.). The highest ability to chelate Fe2+ has been shown by the extract from adzuki bean seeds coat subjected to thermal stress (7.06 %) and the lowest control extract (3.08%).
Conclusions. It can be concluded that only thermal stress contributes to the improvement of antioxidant activity of extracts obtained from adzuki bean seeds coat.

Phenolic compounds of three unconventional Sudanese oils

Background. The total amount and content of phenolic and fl avonoid compounds using the Folin-Ciocalteu and Aluminum chloride methods of the methanolic extracts of Sclerocarya birrea oil (SCO), Melon bug oil (MBO), and Sorghum bug oil (SBO) were studied.
Material and methods. Dry samples of Sclerocarya birrea, Aspongopus vidiuatus and Agonoscelis pubescens were used in this study. The oil was extracted using n-hexane following AOCS method. The phenolic compounds were extracted following a well known method and the total amounts of phenolic and fl avonoids were determined using Folin-Ciocalteau and aluminum chloride methods, respectively and were identifi ed by HPLC.
Results. The concentration of total phenolic compounds was determined as 3.3, 20.7 and 0.9 mg/100 g oil, in SCO, MBO and SBO, respectively, calculated as gallic acid equivalents. The polar fraction of the three oils was separated using solid phase extraction method. The variation of simple and complex oils phenols studied by high-performance liquid chromatography with diode-array detection (DAD) using sephadex eluted by acetone revealed six phenolic compounds which were identifi ed as vanillic acid, callistephin, sinapic acid, t-cinnamic acid, epicatechin, and luteolin in SCO, and four phenolic compounds were identifi ed as vanillin,
sinapic acid, o-coumaric acid, and quercetin, in SBO, while in MBO four phenolic compounds were identifi ed as t-cinnamic, syringic acid, quercetin and pelargonin.
Conclusions. The phenolic compounds found in SCO, SBO, and MBO can be divided into phenolic compounds and fl avonoids.

Studies on the production of alkaline α-amylase from Bacillus subtilis CB-18

Background. Amylases are among the main enzymes used in food and other industries. They hydrolyse starch molecules into polymers composing glucose units. Amylases have potential applications in a number of industrial processes including foods and pharmaceutical industries. Alkaline α-amylase has the potential of hydrolysing starch under alkaline pH and is useful in the starch and textile industries and as an ingredient of detergents. Amylases are produced from plants, however, microbial production processes have dominated applications in the industries. Optimization of microbial production processes can result in improved enzyme yields.
Material and methods. Amylase activity was assayed by incubating the enzyme solution (0.5 ml) with 1% soluble starch (0.5 ml) in 0.1 M Tris/HCl buffer (pH 8.5). After 30 minutes, the reaction was stopped by the addition of 4 mL of 3,5-dinitrosalicylic acid (DNS) reagent then heated for 10 min in boiling water bath and cooled in a refrigerator. Absorbance readings were used to estimate the units of enzyme activity from glucose standard curve. Hydrolysed native starches from cassava, rice, corn, coco yam, maize and potato and soluble starch were adjusted to pH 8.5 prior to incubation with crude enzyme solution. Reducing sugars produced
were therefore determined. The effect of pH on enzyme activity of the alkaline α-amylase was determined by using buffer solutions of different pH (potassium phosphate buffer, 6.0–7.0; Tris-HCl buffer 7.5 to 9.0 and carbonate/bicarbonate buffer, pH 9.5–11) for enzyme assay. The pH stability profi le of the enzyme was determined by incubating 0.5 ml of α-amylase enzyme in 0.1 M Tris/HCl buffer (pH 8.5) and 0.5 ml of 1% (w/v) soluble starch (Merck) in 0.1 M Tris/HCl buffer (pH 8.5) for 3 h in various buffers. The effect of
temperature on enzyme activity was studied by incubating 0.5 mL of the enzyme solution contained in the test tube and 0.5 mL of 1% soluble starch (Merck) solution prepared in 0.1 M Tris/HCl buffer (pH 8.5) for 3 h at various temperatures (25, 30, 35, 40, 45, 50, 55 and 60°C) in a thermo static water bath. The reactions were stopped by adding DNS reagent. The enzyme activity was therefore determined. Thermal stability was studied by incubating 0.5 ml of enzyme solution in 0.1 M Tris/HCl buffer (pH 8.5) and 0.5 ml of 1% (w/v) soluble starch (Merck) in 0.1 M Tris/HCl buffer (pH 8.5) for 3 h at various temperatures (20, 30, 40, 50, 60 and 70°C) for 60 min.
Results. The enzyme displayed optimal activity at pH 8.0 at which it produced maximum specifi c activity of 34.3 units/mg protein. Maximum stability was at pH 8.0 to 9.0. Maximum activity was observed at temperature of 50°C while thermo stability of the enzyme was observed at 40–50°C. The enzyme displayed a wide range of activities on starch and caused the release of 5.86, 4.75, 5.98, 3.44, 3.96, 8.84 mg/mL reducing sugar from cassava, potato, cocoyam, corn, rice and soluble starch respectively.
Conclusion. This investigation reports some biochemical characterization of alkaline α-amylase from Bacillus subtilis CB-18. The substrate specifi cities of this enzyme on various starches suggested that the alkaline α-amylase enzyme had combined activities on raw and soluble starch.

Inhibitory properties of lithium, sodium and potassium o-, m- and p-coumarates against Escherichia coli O157:H7


Background. The aim of this paper was to assess the inhibitory properties of salts of phenolic acids against Escherichia coli O157:H7 ATCC 8739. Escherichia coli O157:H7 is a pathogen which is able to produce verotoxins provoking hemorrhagic diarrhea in humans. There is a strong need for the effective natural methods eliminating E. coli O157:H7 from food.
Methodology. The following salts were tested: sodium, potassium and lithium salts of ortho-coumaric, meta-coumaric and para-coumaric acids. The 1%, 2%, 3%, 4% and 5% water solutions of each substance were prepared. Agar-well diffusion method was applied. Petri dishes were incubated at 35°C for 24 h. At the end of the incubation period, inhibition zones which appeared on the medium Petri dishes were calculated in millimeters.
Results. It was found that lithium salt of o-coumaric acid, potassium salt of o-coumaric acid, lithium salt of m-coumaric acid and sodium salt of m-coumaric acid were most effective towards E. coli O157:H7, while potassium salt of m-coumaric acid, a sodium salt of p-coumaric acid were slightly less effective and lithium salt of p-coumaric acid did not possess any antimicrobial activity.
Conclusion. The salts of phenolic acids having various structural features showed different characteristics towards foodborne pathogens. Such fi ndings indicate that phenolic acids and their salts may be a potential bio-alternative for chemical food preservation.


Assessment of membrane stabilizing activity from honey. An in-vitro approach

Aim. The present study was conducted to evaluate Manofl ora (MF), Polyfl ora (PF), Polyfl ora forest (PFf), and Processed (Pro) honey varieties to compare the in-vitro anti-infl ammatory effects of aqueous honey samples in dose dependent manner. In-vitro anti-infl ammatory activity was evaluated using membrane stabilization assay of RBCs at different aqueous honey concentrations.
Material and method. The present investigation carried out for selected varieties of honey against erythrocytes exposed to both heat and hypotonic lyses and inhibition of membrane damage was compared to the standard drug acetylsalicylic acid.
Results. Membrane damage was inhibited in both the model hemolysis of erythrocytes in vitro in a concentration dependent manner. Hypotonic solution inducing damage was inhibited by aqueous honey sample in ascending order ranged from 8.25% to 97.76% at 10 to 50 mg/ml and standard drug acetylsalicylic acid showing hemolysis protection 96.09% at 100 μg/ml concentration. In heat induced hemolysis model aqueous honey sample exhibited its protecting property during external stress condition in all samples ranged from
0.44% to 21.23% at 10 to 50 mg/ml and acetylsalicylic acid showed 39.38% at 100 μg/ml concentration. Among the variety PFf showed highest protecting nature for hypotonic solution induced lyses (97.76%) and heat induced hemolysis (21.23%) at 50 mg/ml respectively.
Conclusion. With these investigations data conclude that the model exhibits marked anti-infl ammatory effect. Future research is to be carried out to identify the molecules responsible in honey and its mechanism involved.