Nadica Dobričević

Optimization of Ultrasound Assisted Extraction of Functional Ingredients from Stevia Rebaudiana Bertoni Leaves

Abstract The aim of the present study was to reveal an effective extraction procedure for maximization of the yield of steviol glycosides and total phenolic compounds as well as antioxidant activity in stevia extracts. Ultrasound assisted extraction was compared with conventional solvent extraction. The examined solvents were water (100°C/24 h) and 70% ethanol (at 70°C for 30 min). Qualitative and quantitative analyses of steviol glycosides in the extracts obtained were performed using high performance liquid chromatography. Total phenolic compounds, flavonoids, and radical scavenging capacity by 2, 2-azino-di-3-ethylbenzothialozine- sulphonic acid) assay were also determined. The highest content of steviol glycosides, total phenolic compounds, and flavonoids in stevia extracts were obtained when ultrasound assisted extraction was used. The antioxidant activity of the extracts was correlated with the total amount of phenolic compounds. The results indicated that the examined sonication parameters represented as the probe diameter (7 and 22 mm) and treatment time (2, 4, 6, 8, and 10 min) significantly contributed to the yield of steviol glycosides, total phenolic compounds, and flavonoids. The optimum conditions for the maximum yield of steviol glycosides, total phenolic compounds, and flavonoids were as follows: extraction time 10 min, probe diameter 22 mm, and temperature 81.2°C.

Variation in the Bioactive Compound Content at Three Ripening Stages of Strawberry Fruit

During the harvest season of two consecutive years, five strawberry cultivars (‘Arosa’, ‘Elsanta’, ‘Marmolada’, ‘Miss’ and ‘Raurica’), grown in the continental part of the Republic of Croatia, were examined. Strawberry fruits quality was evaluated by individual phenol compounds, individual anthocyanins and fruit color. Fruits were harvested in three different periods. Analyzed strawberry cultivars show very good average values of the studied phenolic acids and flavonoids with predominant caffeic acid and epicatechin content in all researched strawberry cultivars. Considering the content of individual anthocyanins, pelargonidin 3-glucoside is predominant in strawberry extract followed by cyanidin-3-glucoside and pelargonidin 3-rutinoside. The correlation between individual anthocyanin content and chromaticity parameters was detected in all strawberry cultivars, additionally correlation coefficients and statistical significance were much lower. The results show a positive association between cultivar and harvest time on strawberry pulp color, with each of the color variables, a, b, a/b ratio, C, L and h° values.

Ultrasound-assisted extraction of bioactive compounds from lemon balm and peppermint leaves

Abstract The aim of this study was to investigate the influence of conventional and ultrasound-assisted extraction (frequency, time, temperature) on the content of bioactive compounds as well as on the antioxidant activity of aqueous extracts from fresh lemon balm and peppermint leaves. Total phenols, flavonoids, non-flavonoids, total chlorophylls, total carotenoids, and radical scavenging capacity were determined. Moreover, the relationship between bioactive compounds and antioxidant capacity was studied by linear regression. A significant increase in all studied bioactive compounds during ultrasonic extraction for 5 to 20 min was found. With the classical extraction method, the highest amounts of total phenols, flavonoids, and antioxidant activity were determined, and the maximum amounts of total chlorophylls and carotenoids were determined during 20 min ultrasonic extraction. The correlation analysis revealed a strong, positive relationship between antioxidant activity and total phenolic compounds.

The change of fruit quality parameters in day-neutral strawberries cv. Diamante grown out of season

This research was conducted on the strawberry cultivar Diamante in continental parts of Croatia. The experiment was designed as four replicates with 100 plants for each harvest time. The quality of strawberries cv. Diamante grown out of season (fruit were picked in the early morning hours at three harvest times: 27 June, 7 September, 28 October) was determined. Total soluble solids (°Brix) ranged from 5.00% to 7.03%, total acidity ranged from 1.05% to 1.12%, total soluble solids/acidity ranged from 4.74 to 6.34, vitamin C ranged from 40.73 mg/100 g fresh weight to 46.68 mg/100 g fresh weight, pH ranged from 3.53 to 3.72, total phenols ranged from 276.48 to 326.76 mg/l, non-flavonoids ranged from 169.50 to 260.53 mg/l, and flavonoids ranged from 44.71 to 106.53 mg/l, respectively. In addition, total anthocyanins ranged from 15.95 to 21.70 mg/l. The lightness L values of fruits ranged from 30.24 to 41.05, chroma C values from 25.92 to 34.13, and Hue angle H values from 44.51 to 56.02. The data showed that cv. Diamante grown out of season is of satisfactory quality.

Quality of strawberries produced applying two different growing systems

The quality of strawberry fruits (cv. “Clery” and cv. “Asia”) was studied and compared under the conditions of two different growing systems (under a high plastic tunnel and in the open field). Several chemical parameters were determined in the harvested fruits: dry matter, soluble solids, total acidity, ratio between sugars and acids, vitamin C, total phenols, non-flavonoid phenolic compounds, total anthocyanins, reducing sugars, sucrose, colour of fruits, and HPLC analysis of flavonols, flavanols, and phenolic acids content. The fruits of cultivar “Clery” had more antioxidant compounds than the fruits of cultivar “Asia” when grown in the open field. The fruits of both cultivars grown under a tunnel generally had good properties; however, the total phenol content and the non-flavonoid fraction were somewhat lower. Among the phenolic compounds, (+)-catehin, (−)-epicatehin, ellagic, p-coumaric acid, quercetin, and kaempferol were identified and quantified using HPLC equipped with Photo Diode Array detection. The highest content of phenolic compounds was found in cv. “Clery” from the open field production. Analysis of antioxidant compounds has not shown statistically significant differences as a result of growing system or grown cultivar. Samples of strawberries grown under a high plastic tunnel, regardless of examined cultivar, had better basic chemical parameters. The mash colour also depends on cultivar and growing system.

Antioxidant Potential of Fruit Juice with Added Chokeberry Powder (Aronia melanocarpa)

The purpose of this study was to determine the possibility of using chokeberry powder as a supplement in apple juice to increase the nutritional value of the final product with the aim of developing a new functional food product. Also, to determine the influence of ultrasound assisted extraction on the bioactive compounds content, nutritional composition and antioxidant potential of apple juice with added chokeberry powder. The juice samples with added chokeberry powder had higher antioxidant capacity, irrespective of the extraction technique used. Apple juice samples with added chokeberry powder treated with high intensity ultrasound had significantly higher content of all analyzed bioactive compounds. The application of high intensity ultrasound significantly reduced the extraction time of the plant material. A positive correlation between vitamin C content, total phenols, flavonoids and anthocyanins content and antioxidant capacity was determined in juice samples with added chokeberry powder treated with high intensity ultrasound.

Bioactive compounds, pigment content and antioxidant capacity of selected cabbage cultivars

Abstract The main aim of this research was to determine the amount of bioactive compounds and antioxidants, as well as differences in chemical composition between six cabbage cultivars. Also, the amount of pigment compounds and relationship between chromaticity parameters between selected cabbage cultivars was determined. The significant differences (p≤0.0001) of all analyzed chemical parameters were determined. According to the obtained results of pigment composition, white cabbage cultivars contained the higher amounts of total chlorophylls (average 3.15 mg g-1 fresh weight), while red cabbage cultivars contained the higher amounts of anthocyanins (average 696.08 mg kg-1 fresh weight). Red cabbage cultivars contained the higher amounts of biologically active compounds. Average values of total phenols, total flavonoids, non-flavonoids and vitamin C were as follows: 172.45 mg GAE 100 g-1 fresh weight, 88.88 mg GAE 100 g-1 fresh weight, 83.59 mg GAE 100 g-1 fresh weight and 28.49 mg 100 g-1 fresh weight. Higher antioxidant capacity was determined in red cabbage cultivars. On average, in red cabbage cultivars even 3.9 times higher antioxidant capacity was determined compared to the selected white cabbage cultivars.