Chemical and fruit skin colour markers for simple quality control of tomato fruitsVesna Bukovac
, Tatjana Unuk
, 2015, original scientific article
Abstract: The orientation of this research was to evaluate the classic parameters regarding the external and internal quality of tomato fruits cv. ‘Brilliant‘ at different stages of maturity and to define the dynamics of their changes during the ripening in storage at 18 °C. Principal component analysis (PCA) and multivariate canonical discriminant analysis (DA) were used to classify tomato samples according to quality (internal and external) and nutritional value based on fruit mass, fruit skin colour, contents of soluble solids (SS), total titratable acids (TTA), ascorbic acid (AA), and total antioxidant potential (TAP). Several methods are usedfor determining AA content and TAP in plant samples. A simple routine method, direct redox titration with iodate solution and spectrophotometric determination of TAPSP, as described by Singleton and Rossi, also called total phenols, were used respectively. The results show that the stage of maturity (based on fruit skin colour) strongly determines the quality and nutritional value of the tomato fruit. Tomatoes harvested at table maturity (red colour, index a*/b* ≥ 0.85) have a significantly higher nutritional value (in terms of antioxidants – TAPSP and AA content) and overall quality than those harvested at an earlier maturity stage and then ripened in storage. This brings out the importance of short food supply chains and, from the viewpoint of overall fruit quality, it raises doubt about harvesting before reaching table maturity. On the other hand, it is necessary to be extremely attentive when determining optimal maturity, because when the plant becomes over-ripe or when stored, the nutritional value and overall quality decrease drastically. Besides the colour parameters, AA content is the most important chemical marker for a simple quality control. By using a simple and reliable analytical method for determining AA content, such as direct redox titratiation, the monitoring of tomato fruit quality could also be easily performed in situ.
Keywords: chemical markers, quality control, antioxidant, tomato, discriminant analysis
Published: 24.10.2017; Views: 697; Downloads: 110
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Strawberries from integrated and organic productionJanja Kristl
, Andreja Urbanek Krajnc
, Branko Kramberger
, Silva Grobelnik Mlakar
, 2013, original scientific article
Abstract: As the nutritional quality of food is becoming increasingly more important forconsumers, significant attention needs to be devoted to agricultural practices and their influences on the nutrient contents in food. The presentedinvestigation studied the mineral contents and antioxidant activitiesin the fruits of four organically-grown strawberry cultivars 'St. Pierre', 'Elsanta', 'Sugar Lia' and 'Thuchampion' when compared to those of integrated-grown plants. The strawberries were digested and analyzed for K, Mg, Fe, Zn, Cu, and Mn using an atomic absorption spectrometer, whilst P was analyzed using a vanadate-molybdate method. In addition, antioxidant activity was estimated by using the ABTS assay. The results showed that the mineral contents and antioxidant activities in strawberries depends on the cultivar, and its production system. Organically-grown fruits showed higher antioxidant activities and Cu content than the integrated fruits, whilst the integrated fruits were superior in their contents of P, K, Mg, Fe and Mn. All the cultivars showed similar Zn content, probably reflecting the fact that the Zn content in strawberries does not depend on the cultivar.
Keywords: strawberries, minerals, antioxidant activity, production system
Published: 30.12.2015; Views: 783; Downloads: 102
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Potential of phenolic antioxidantsIva Ružić
, Mojca Škerget
, Željko Knez
, 2010, review article
Abstract: In vitro studies have shown a link between the consumption of food rich in (poly)phenols, especially flavonoids, and reduced risk of coronary heart diseases. Several flavonoids have been reported to prevent low density lipoprotein cholesterol oxidation in vitro. The aim of our work was to determine antioxidant and radical scavenging activity of flavonoids myricetin,quercetin, rutin, luteolin, apigenin, kaempferol, catechin, epicatechin and epigallocatechin gallate and to study the influence of chemical structure and flavonoid interactions on the ability to inhibit oxidation and scavenge free radicals. Two in vitro methods, i.e. oxidation of â-carotene in an emulsion system and DPPH (1,1-Diphenyl-2-picrylhydrazyl) radical scavenging assay, were applied. In addition, a review of in vivo studies that investigate the effectiveness of food flavonoids in reducing oxidative damage in human body was done and their results were analyzed and compared to in vitro results obtained in our laboratory. Although all tested flavonoids except apigenin showed strong antioxidant and antiradical properties in vitro, these findings can not be completely confirmed from the reviewed in vivo human studies since those results are sometimes contradictoryand inconsistent.
Keywords: phenolics, flavonoids, antioxidant activity, antiradical activity
Published: 10.07.2015; Views: 777; Downloads: 47
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GRAPE ANTIOXIDANTS - INFLUENCE OF PROCESSING PARAMETERS ON THEIR CONTENT AND ACTIVITYIva Ružić
, 2012, dissertation
Abstract: Grapes and wine production residuals, containing grape skins, seeds and stems, represent important sources of phenolic compounds. Red wines are rich in phenolic antioxidants while white wines generally show lower (poly)phenolic content and antioxidant activity. The main difference in the production of white and red wines is the fermentation step. The fermentation of red grapes includes maceration, i.e. it takes place in both liquid and solid parts of the grape. In the case of white wines, the must is clarified before the fermentation starts, cultured yeasts are added to convert the must to wine and antioxidant sulfur dioxide is inserted to protect the wine.
The objective of the PhD research was to study antioxidant potential of white grape phenolics both in raw material and fermentation products. First, the standards of phenolic compounds commonly found in white grapes and wines were tested for their antioxidant and antiradical activity. All tested compounds except apigenin showed strong antioxidant and antiradical properties. Afterwards, conventional solid-liquid extraction (CE) and pressurized liquid extraction (PLE) of phenolic compounds from grape seeds were performed. The optimal extraction conditions were investigated and extracts were analyzed in order to determine their total phenolic content, individual phenolic compounds and antiradical potential. Two different drying methods (hot air and freeze drying) were applied to the seeds. Solvent efficiencies of water, ethanol and water-ethanol mixtures were compared at different temperatures. In addition, supercritical fluid extraction (SFE) with CO2 was investigated as the technique for the recovery of phenolic compounds and for the pretreatment of white grape seed samples. Both CE and PLE gave extracts rich in phenolic compounds with good antiradical properties and, generally, the best results were obtained with PLE at 130°C. At the end, the influence of maceration process on the content and the activity of grape phenolic antioxidants in white wines was studied. For such a purpose, six commercially available macerated white wines from Italy and Croatia were analyzed. In addition, eight non-macerated wines from the same region and variety were studied and compared to macerated wines. The experiments have shown that the maceration process increases the total phenolic content and antiradical activity of the wine. It enables the production of white wines rich in phenolic compounds and with strong antiradical properties in completely natural way using only the grapes and without addition of any chemical agents.
Keywords: white grapes, white wine, maceration, antioxidant activity, polyphenols, extraction, PLE, SFE.
Published: 05.04.2012; Views: 2242; Downloads: 125
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Properties of Mint as a Food PreservativeRok Penko
, 2011, undergraduate thesis
Abstract: This study was designed to evaluate antimicrobial and antioxidant activities of the mint extracts from Mentha piperita L. and Mentha aquatica L. In vitro antibacterial activity against two foodborne bacteria (Listeria monocytogenes, Staphylococcus aureus) was evaluated by the well diffusion method. The activity was assessed by the diameter of the inhibition zone. Four of the five extracts from Mentha piperita were active against S. aureus, but none of the extracts was active against L. monocytogenes. Extracts obtained from Mentha aquatica showed no activity against both foodborne bacteria. The horseradish peroxidase/guaiacol assay was used to investigate in vitro antioxidant activity of two mint extracts (Mentha piperita and Mentha aquatica). The ascorbic acid was tested as a reference compound with known antioxidant activity to validate our approach. Extracts from Mentha aquatica showed strong antioxidant activity, but on the other hand, extracts from Mentha piperita showed no antioxidant activity.
Keywords: preservatives, Listeria monocytogenes, Staphylococcus aureus, antimicrobial activity, antioxidant activity, mint extracts
Published: 21.04.2011; Views: 2181; Downloads: 102
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