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Atomic absorption spectrometry is a powerful technique for determination of tin in canned foods. Homogenous samples of syrup and solid parts were digested by means of microwave digestion system MLS 1200 MEGA where hydrochloric and nitric acid were used as reagents. The measurements were carried out using a Perkin-Elmer AAnalyst 700 atomic absorption spectrometer. Detection limit was 4 mg/kg in nitrous oxide and acetylene flame. There were analysed 222 samples of 26 various kinds of canned fruit (e.g. pineapple, peach, mandarin), vegetables (e.g. bean, mushroom, tomato) and meat (sea products) in this work. The analytical results indicated tin total concentrations from under 4 mg/kg to 353 mg/kg. Different concentrations of tin between syrup and fruit were observed. The concentration of tin was higher in solid parts than in syrup. Relationship between the concentration and time period after opening was studied. The corrosion of the tinplate surface was accelerated by air and the amount of dissolved tin was significantly increasing in syrup as well as fruit when cans were opened and stored for two days at 6°C.

Total starch (TS), amylose and resistant starch (RS) were determined in the sets of smooth pea and wrinkled pea varieties in the years 2006-2008. Starch content of smooth peas varied in the range 53.61-57.23%. Average amylose content was 27.8%. Resistant starch content varied from 2.07% to 6.31%. Content of starch at wrinkled pea varied from 26.57% to 32.55%. Average amylose content was 76.82% of total starch. Content of total starch increases continually during seed development. The dependence of total starch on determined dry mass in harvested sample can be defined by equation γ = 1.2427 × -6.5611, by determination coefficient R² = 0.8936 and highly significant correlation coefficient r = 0.945. Total starch content in dry seed reached final average value 29.56%. In garden pea, the level of maturity (by tenderometric measurement) and dry matter were determined. Resistant starch content of 11 garden pea cultivars was studied in three different terms of technological harvest.

The manipulation of grape yield is widely practised to improve grape and wine quality. Merlot and Cabernet Sauvignon vines in the Zagreb vineyard hills, north-western Croatia, were subjected to three crop removal treatments [cluster thinning (CT), berry thinning (BT), CT+BT, and untreated control] in a randomised block design experiment. CT and CT+BT treatments reduced the grape yield but increased the mean cluster weight compared to control vines. BT alone had a little effect on the yield components. Control grapes generally had the lowest soluble solids (°Oe) and highest titratable acidity (g/l). In most cases, control wines had the lowest total phenols, flavan-3-ols, and anthocyanin concentrations, while CT+BT treatment had the highest ones followed by CT treatment. It was concluded that CT+BT produced wines with generally increased total phenols, flavan-3-ols, and anthocyanins, as well as many individual phenolic compounds. Thus, grape yield per vine seems to be strongly connected with the grape and wine compositions. The final cost-effectiveness of this canopy interventions still remains questionable.

The objective of this research was to evaluate the effect of blackcurrant mash blended with apple pulp during juice production and storage on its phenolic composition, antioxidant activity, L-ascorbic acid, and colour. Five variants of samples were prepared: apple juices from two cultivars: the Shampion and Idared cultivars without and with 20% of blackcurrant pulp and blackcurrant juice which were stored at 4°C and 30°C for 6 months. The apple juices prepared from the Idared and Shampion cultivars had a very low L-ascorbic acid contents (1.32 mg/l and 6.26 mg/l, respectively) whereas blackcurrant juice showed the highest amount of L-ascorbic acid, i.e. 704.3 mg/l. The addition of 20% of blackcurrant pulp before apple crashing resulted in a great difference between L-ascorbic acid contents in juices. The addition of blackcurrant fruits before apple crushing had a statistically significantly different (P < 0.05) influence on phenolic compounds, especially in Idared blended pulp. As compared with the control samples, flavan-3-ol concentration increased 4 times in juices made from 80% of Idared apples blended with 20% of blackcurrant fruits. Apple pulp blended with blackcurrant was richer in hydroxycinnamic acids (especially caffeic, p-coumaric, and neochlorogenic acids) than juices made only from apples. The results ranged from 83.05 to 3297.6µM T/100 ml for DPPH (1,1-diphenyl-2-picrylhydrazyl radical), from 20.64 to 490.93µM T/100 ml for ABTS (2,2'azinobis-(3-ethylbenzthiazoline-6-sulphonic acid)), and from 1.52 to 37.35µM T/ml for FRAP (Ferric reducing antioxidant power assay) for apple juice made from the Idared cultivar and for blackcurrant juice, respectively. The highest level of the antioxidant capacity (P < 0.05) observed in the blackcurrant sample was due to the effect of the high anthocyanin and ascorbic acid contents. The apple juice colour showed a moderate degradation with time as indicated by the slight reduction of L* values in the samples stored at 4°C for 6 months, and a much higher decrease of L* values in the samples stored at 30°C. The lightness of the apple blended with blackcurrant increased during storage as a result of the coloured anthocyanin degradation. The temperature during the sample storage (30°C) had a significant influence, resulting in a higher degradation of all phenolics compounds analysed, colour and antioxidant activity.

Green vegetables are considered an important source of some nutritionally important constituents that have health benefits (e.g. vitamins, minerals, antioxidants, fibre). Epidemiological data suggest that consuming a diet rich in fruit and vegetables can lower the risks for chronic diseases, such as cardiovascular diseases and cancer. Over the past 100-150 years, there have been enormous increases in the consumption of omega-6 fatty acids due to the increased intake of vegetable oils from various seeds. Studies have indicated that a high intake of omega-6 fatty acids shifts the physiological state to one that is prothrombotic and pro-aggregatory, whereas omega-3 fatty acids have anti-inflammatory, antithrombotic, anti-arrhythmic, hypolipidemic and vasodilatory properties. Literature data regarding the contents of higher fatty acids (e.g. omega-6 fatty acids) in vegetables are scarce, although vegetables are known to contain a high proportion of n-3 fatty acids. Here, the fatty acid content and composition was determined for 26 green vegetables that are commonly available in Slovenia, by gas-liquid chromatography and in situ transesterification. The fatty acid analysis revealed C16:0, C16:1, C18:0, C18:1, C18:2n-6 and C18:3n-3. The total fatty acid content in the vegetables ranged from 500 mg/100 g fresh weight (f.w.) in red cabbage, to 4.000 mg/100 g f.w. in tarragon. The proportion of saturated fatty acids (as g/100 g total fatty acids) ranged from 12% to 35%. All of the vegetables contained a high proportion of poly-unsaturated fatty acids (PUFAs), ranging from 45% to 81% of total fatty acids. The omega-3 PUFA proportion ranged from 5% in carrot to 60% in tarragon. The content of mono-unsaturated fatty acids ranged from 1% to 25%. French beans, tarragon and radish sprouts contained the highest concentrations of C16:1, at 5 mg/100 g f.w. Consumption of 100 g of tarragon meets 13.2% of daily requirements for α-linolenic acid; similarly, for radish sprouts 9.4%, for mangold 6.9%, for ruccola 5.4%, for green salad 5.0%, and for kale 4.7%. Green vegetables are an important source of 18:3n-3 PUFAs, especially for vegetarian populations.

Wheat, apple, potato, and bamboo fibres were applied at 1 and 3% content to bread wheat flour and these additions were studied for the quality of dough and bakery products characterised by farinograph parameters, laboratory baking tests, firmness, and sensory analysis. The addition of fibre caused a decrease of loaf volume, also a change of crumb colour and a slight increase of bread crumb firmness. On the other hand, the addition of fibre affected the farinograph parameters, significantly decreased the specific volume especially at 3% fibre (P < 0.05). A statistically significant difference (P < 0.05) in firmness was found out between products with added wheat and bamboo fibre. Statistically highly significant differences (P < 0.001) were found among the other pairs of products with fibre. The best sensory properties were detected when examining the products with an addition of wheat and potato fibre. The enrichment of bread with fibre at 1% or 3% increased the dietary fibre content in bread with slightly adverse effects on bread quality.

We investigated the changes in omega 3 enriched carp fillets caused by pan frying. The investigated characteristics were fat uptake, fatty acid (FA) composition, and oxidation. Four different fats were used and fillets were fried plain or battered. The fillet fat content increased during frying and FA composition in the fillets reflected the composition of the frying fat. Frying with sunflower oil negatively influenced the nutritional value by decreasing the n-3/n-6 ratio in the fillets. Frying with rapeseed oil preserved the favourable n-3/n-6 ratio without increasing the saturated fatty acids (SFA). Frying with lard and butter preserved the n-3/n-6 ratio but increased the SFA content. No increased oxidation occurred with the use of rapeseed oil. We concluded that using rapeseed oil for fish seemed to preserve the nutritionally valuable composition best.

The goal of this study is the evaluation of enriched bread prepared with an addition of buckwheat as a source of biologically active components in nutrition. Experimental pastry was baked using buckwheat wholegrain flour blended with wheat flour in different portions (10%, 20%, 30%, 40% and 50%) in order to observe the influence of buckwheat addition on dough processing and the quality of the final baked products. Taking into account the overall acceptability rating, it was concluded that bread with an addition of up to 30% of buckwheat could be baked with satisfactory evaluation results. The content of rutin in loaves in a consumable form prepared with a buckwheat addition varied between 7.76 mg/kg and 26.90 mg/kg. The clinical study which followed the baking experiment was based on the consumption of enriched bread (30% buckwheat, between 34.7 mg/kg and 38.2 mg/kg rutin content in dry matter) by a group of volunteers during a period of four weeks. The results approved the increase of the total antioxidant status thanks to the buckwheat enriched bread consumption from the value of 1.135 ± 0.066 mmol/dm³ at the beginning of the study to 1.46 ± 0.083 mmol/dm³ at the end of the study, i.e. significant differences.

Bile salt hydrolase (BSH) activity of intestinal bacteria (including lactobacilli) is one of the indirect ways of decreasing a cholesterol level in human body. Tested Lactobacillus strains were isolated from various sources (faeces of fully breast-fed infants, cow's colostrum, cow's raw milk cheeses, and cow's raw milk) and identified by genotypic and phenotypic methods. All strains, including three commercial probiotic strains and six culture collection strains, were subsequently tested for their BSH activity via two methods - thin layer chromatography (TLC) and plate assay. Among all the 59 Lactobacillus strains, 15 strains were shown to be BSH positive by TLC method and only 8 of them by plate assay. Most of the BSH positive strains (9 strains) were isolated from faeces. Differences between BSH activities for sodium salts of cholyltaurine and cholylglycine were demonstrated. The TLC method was shown to be more sensitive compared to the plate assay for BSH activity determination.

We investigate the effects of consumption of MRPs from the glucose-lysine model system heated 15°C-90 min on protein digestibility and its utilisation in young (3-week) and adult (12-week) rats. Nitrogen faecal excretion significantly increased after MRP consumption, especially during the third week. Protein digestibility was lower in both age groups studied, but the utilisation was unaffected. Parallelly, the nitrogen retention and its net utilisation for the entire experimental period did not vary. In young rats the faecal nitrogen exceeded the amount of ingested nitrogen coming from MRPs, suggesting that digestibility of undamaged nitrogen was affected. The same action is suspected in adult animals, but the results were not quantitatively conclusive, and therefore the effect should be moderate in this period.

The preparation of mango wine by yeast-mango peel immobilised biocatalyst system by repeated batch fermentation was conducted and compared to free cells fermentation at 15, 20, 25, and 30°C. The operational stability of the biocatalyst was good as the ethanol concentrations (76.0-96.0 g/l) and productivities (1.53-3.29 g/l/h) were high, showing the suitability of the biocatalyst for even low temperature winemaking. The concentration of ethyl acetate was not above 40 mg/l in all cases, and higher alcohols were low (< 330 mg/l) in wine with immobilised cells indicating an improvement in the product compared to free cells fermentation. Amyl alcohols were proved to be temperature dependent and decreased with the decrease in temperature (262.48-146.83 and 239.74-184.34 mg/l) in the case of fermentation batches with immobilised and free cells, respectively, from 30°C to 15°C. Sensory evaluation revealed fruity aroma (7.9 ± 0.73), fine taste (7.7 ± 0.24), and the overall improved quality of the wines produced by the immobilised system.

3-alkyl-2-methoxypyrazines (MPs) represent an important and potent class of odor-active compounds associated with wine quality. 30 ng/l each of 3-isobutyl-2-methoxypyrazine, 3-isopropyl-2-methoxypyrazine and 3-secbutyl-2-methoxypyrazine were added to a Riesling and Cabernet Franc wine and monitored with HS-SPME-GC-MS over 18 months to investigate the effects of various closure and packaging options as well as light and storage temperature on MPs. Other impact odorants were monitored using SPE-GC-FID. Changes in MP concentrations during bottle aging varied with closure/packaging option, with the greatest decrease evident in Tetrapak® cartons. We observed similar changes in other impact odorants to previous studies, with synthetic corks displaying an increased capacity for sorption compared to natural corks and screwcaps. MPs did not vary consistently over time with light or temperature conditions. Acetate esters decreased, regardless of light or temperature conditions, while phenethyl acetate and isoamyl acetate decreased at a greater rate in ambient temperature conditions compared with 12°C. Free and bound SO₂ retention was higher in light-excluded conditions and influenced by bottle hue.

The antilisterial activity of E. mundtii 1282 strain and its cell-free neutralised supernatant was observed against five persistent L. monocytogenes strains using the agar spot method. The enterococcal metabolite was consequently characterised as a proteinaceous substance - the bacteriocin-like substance, which was heat-stable at heating to 100°C for 30 min, stable at pH 2-12, and still active after eight-week long storage at 6°C and -20°C. The bacteriocin-like substance reached the highest activity of 6400 AU/ml after ten hours of cultivation of E. mundtii 1282 strain, when it was at the stationary phase of its growth. E. mundtii 1282 strain produced the bacteriocin-like substance: in BHI broth with pH 4-6, at the cultivation temperature 12-45°C, and in BHI broth with 1-6% (w/w) NaCl.

The levels are reported of the free 3-chloropropane-1,2-diol (3-MCPD), its bound forms, the recognised precursors of 3-MCPD, and the factors influencing its formation in 5 selected coffee surrogates and 18 malts in the Czech Republic. The coffee surrogates had the free 3-MCPD level in the range of < 9.0 to 32 µg/kg while the highest amount was found in roasted barley. In malts, the free 3-MCPD levels were similarly low (< 9.0 to 45 µg/kg) being the highest in roasted malts (16-45 µg/kg). Nevertheless, the values found in either surrogates or malts, calculated after normalisation to 40% dry matter content, did not exceed the European Union limit of 20 µg/kg adopted for soy sauces and acid-HVP. The risk for consumers could arise from the bound 3-MCPD, its elevated levels having been found in both coffee surrogates and malts. In coffee surrogates, the bound 3-MCPD levels varied between 145-1184 µg/kg product; the highest level was found in roasted barley. The bound 3-MCPD levels exceeded the free 3-MCPD levels 32 to 81 times. In malts, the bound 3-MCPD levels ranged from 4.0-650 µg/kg, the highest amount having been found in roasted malts (463-650 µg/kg). The bound 3-MCPD levels exceeded the free 3-MCPD levels 0.4 to 36 times.

Colour and texture are very important quality properties of all foods. In this work, the influence was investigated of different types of pectin on colour and textural properties in strawberry jams and low-calorie strawberry jams containing fructose and aspartame or fructose syrup and aspartame. The highest anthocyanin content and total phenol content were detected in strawberry jam samples prepared with low methoxy amidated pectin. During storage, after 4 and 6 weeks at both storage temperatures, room temperature and 4°C, anthocyanin content and total phenol content decreased. Also, free radical scavenging activity decreased during storage. As far as the texture parameters are concerned, namely firmness, consistency and cohesiveness, the highest values were found in strawberry jam samples prepared with high methoxyl pectin.

A collection of lactic acid bacteria (38 Enterococcus and 41 Lactobacillus strains) was tested for the antilisterial activity against 15 Listeria spp. strains (two L. monocytogenes, one L. ivanovii and 12 L. innocua strains) using agar spot method. Out of all 79 bacteria only six Enterococcus strains (1/3A, 3/3A, 6/4D, 6/1A, 1282 and EN3) exhibited antilisterial activity against almost all used indicator strains, when their live cells were tested. When their cell free neutralised supernatants (CFNS) were tested against four selected indicator strains (L. innocua Ln-03, Ln-06, Ln-10 and L. monocytogenes CCM5576) only two Enterococcus spp. strains were active - E. faecalis 6/1A strain from raw cow milk of minor interest due to the activity of its CFNS only against L. innocua Ln-06 and thermolability of the compound and E. mundtii 1282 strain from goat raw milk with CFNS active against 13 Listeria spp. strains including L. monocytogenes. E. mundtii 1282 strain produced probably a bacteriocin, because it completely lost the activity after treatment CFNS with proteinase K.

The hygienic indicators and chemical composition of Prgica cheese produced from raw and pasteurised milks as well as the microbiological quality of dry red pepper used in the cheese production were investigated.. Prgica cheeses and originally packed dry red peppers were collected from five family farms and five vacuum-packed Prgica cheese samples were purchased from the supermarkets. Significantly lower fat (P < 0.01), protein, and total solids contents (P < 0.0001) of artisanal Prgica cheese in comparison to Prgica cheese purchased from the supermarkets were detected. Two samples of cheese produced on family farms and three samples purchased from the supermarkets had high numbers of yeasts and moulds. The yeasts Mucor sp. and Candida famata, and moulds Aspergillus niger and Aspergillus ochraceus, were detected in dry red pepper. The results showed that there was potential yeast and mould contamination among the Prgica cheeses produced from raw milk, as well as Prgica cheeses purchased from the supermarkets, produced from pasteurised milk under controlled conditions, also contained high numbers of yeasts and moulds probably due to contamination by dry red pepper used in their production.

Chlorpropham is employed worldwide as an anti-sprout chemical to the harvested potato tubers during storage. A simple and precise analytical technique is developed for routine estimation of the sprout suppressant from a large number of potato samples supplied from commercial stores demanding quick analysis. Chlorpropham is extracted completely from potato tubers by intelligent reflux extraction followed by quantification using GC-FID (Gas Chromatography-Flame Ionization Detector) equipment. In this article, the performance of the technique is compared with the lengthy extraction/cleanup process, and the results are validated as per one-way analysis of variance. The recommended technique is found to offer rapid, accurate, and reliable analytical results with ease in handling a large number of samples constituting a wide range of residual chlorpropham levels often found in a complex structural commercial potato stores.

The whole buckwheat flour (WBF) was used in Turkish flat bread, lavaş, up to 30% level without gluten, and up to 40% level with gluten and sodium stearoyl-2-lactylate (SSL) additions. Some physical, chemical, and sensory properties of lavaş bread samples were determined. While ash, crude fiber, phytic acid (PA), Fe, K, Mg, and P contents of lavaş breads increased with WBF addition, gluten supplementation caused an increase especially in protein and Ca contents. Leavening process decreased PA contents in the breads compared to raw material, but WBF substitution increased PA contents up to 729 mg/100 g. As a result, the utilisation of WBF in lavaş bread improved the nutrients contents of the bread except PA. The dark colour and slight bitter taste of the WBF affected the sensory score of lavaş bread negatively at 40% substitution level, but the overall acceptability values did not change significantly (P < 0.05) compared to control sample.

The main chemoprotective polyphenolic compounds in the Vitis vinifera berries, rachis, and pedicels of 10 cultivars classified for the production of wine and growing in Southern Moravian vineyards, the Czech Republic, were studied. The following compounds were determined in the frozen fresh berries: gallic acid (1.8-13.3 mg/kg), catechin (70.3-659.1 mg/kg), epicatechin (67.1-237.2 mg/kg), trans-resveratrol (0.1-1.5 mg/kg), and pterostilbene (in traces); in the freeze-dried rachis and pedicels: rutin (10.5-68.6 mg/kg), isoquercitrine (29.8-218.3 mg/kg), catechin (283.7-2227 mg/kg), epicatechin (47.2-215.2 mg/kg), trans-resveratrol (2.6-37.1 mg/kg), and pterostilbene (0.01-0.13 mg/kg), respectively. The contents of polyphenolic compounds were different in various cultivars. The highest levels of catechin and epicatechin were found in the grapes of cv. Blauer Burgunder (3195 mg/kg), in which the second highest content of trans-resveratrol (33.2 mg/kg) was also found. The content of pterostilbene in the whole berries or stems was estimated for the first time. The rachis and pedicels could serve as a prospective source of polyphenolic compounds.

Combined culture of lactic acid bacteria (Lactobacillus brevis, L. plantarum i L. sanfranciscencis) and baker's yeasts was used in order to reduce immunoreactivity of gluten from wheat. Flour and dough samples were analysed in terms of lactic acid fermentation and thermal processing. Their immunoreactivity was determined with ELISA method using both anti-gliadin antibodies from patients suffering from coeliac disease and rabbit anti-QQQPP peptide (main epitope of flour allergen) antibodies. Also, immunoreactivity was measured in the final products after simulated digestion. The obtained total effectiveness of the fermentation and digestion processes amounted to less than 30% relative to immunoreactivity of human anti-gliadin antibodies and less than 10% relative to immunoreactivity of anti-QQQPP peptide antibodies as compared to the baking made with non-fermented flour.

Experimental samples simulated the composition of vermouths. In all experiments, 0.01% quinine was used as a standard bitter substance. Sucrose increased the acceptability in the concentration range of up to 14%, remaining constant at higher concentrations, both in aqueous and 16% ethanolic solutions. A decrease of bitterness was observed in water but not in 16% ethanol. Ethanol did not affect the sweetness appreciably at the concentrations of up to 16%, but 32% ethanolic solutions appeared less sweet. Ethanol enhanced the bitterness only at high concentrations; interactions were similar in the samples containing 10% and 16% sucrose. Aspartame and Neotame sweetness increased the acceptability and decreased the bitterness similarly to sucrose, both in aqueous and in 16% ethanolic solutions.

A precise design of the equipment for thermal sterilisation of rice, potato starch, and oat flakes by dry heat requires the knowledge of the relevant values of physical properties of these products. Water activity and enthalpy are presented as functions of temperature and humidity. Water activity was measured as a function of the moisture content and temperature in the desorption process that reproduces the real conditions existing during dry heat processing in the pilot rotating steriliser equipment. The heat of evaporation can be predicted from these data as a function of the moisture content of these products. DSC (differential scanning calorimetry) method was used for measuring the enthalpy of these products as a function of temperature during desorption of moist products starting from various levels of the moisture content. The total energy Ec necessary for heating the product and evaporation of the given amount of water can be calculated.

The aim of the study was to describe the distribution of total mercury in the tissues of fish originating from important Czech fishing locations and to determine the level of methylmercury as a percentage of total mercury (Hg speciation). At six important fishing locations a total of 144 fishes of 13 species were caught and analysed. Samples of muscle, liver, gonads and scales were analysed for total mercury and in the case of muscles for methylmercury concentrations. Total mercury was determined by AAS using an AMA 254 analyser, and methylmercury determination was performed by GC/ECD using a GC-2010A chromatograph. Total mercury concentrations in muscle and other tissues of all the fish from all fishing locations were below 0.5 mg/kg, with the exception of 6 asps (Aspius aspius). A significant (P < 0.05) correlation was found between the total mercury concentrations in scales and other tissues. Methylmercury made up about 46-100% of total mercury in muscle. The overall results confirmed the good hygienic quality of fish from important Czech fishing locations.

In brewing, yeast may be reused many times. A number of yeast repitchings differs significantly among the breweries. Adjusting the number of times a strain may be serially repitched is of great importance for quality and consistency of final products. The fermentative and physiological characteristics of the yeast culture used in successive laboratory scale fermentations were determined. Yeast physiological state was assessed by the measurement of the levels of intracellular carbohydrates. In our investigation there were not any detectable changes in yeast capacity to ferment. No significant variation in the production of flavour compounds was found either. However, intracellular glycogen and trehalose contents were dependant on the yeast strain, generation number and wort gravity. Nevertheless, an alteration in the yeast physiological condition during serial repitchings occurred in a different mode than in previous studies confirming that the impact of serial repitchings is strain and medium dependent to a large extent.

Yellow, orange, red and brown pigments are formed by air oxidation of single polyphenols or by thermal degradation of sugars to caramels. Caramels increase their colours during anaerobic heating or decrease them by air oxidation. Epicatechin and caramel undergo reversible redox reaction followed by degradation and/or polymerisation at beer aging. That is why both of these colour compounds, besides acting as acid/alkali indicators, can also represent redox indicators that gradually become irreversible. These reactions are accelerated by transient metals or buffering solutions and are therefore more distinct in tap or brewing water than in deionised water. The kind of the brewing water then predetermines not only the beer attributes but also the course of beer aging. Coloured pigments can be partially bleached by reducting agents such as yeast oxidoreductase enzymes and the colour can be then recovered by oxidation; this depends on their polymerisation degree. Methylene blue and methyl red can be used as artificial oxidation-reduction indicators for the study of the redox potential changes because they act reversibly or irreversibly under aerobic or anaerobic conditions, respectively.

We investigate the biostability of phenolic acids from a kenaf (Hibiscus cannabinus L.) seed extract using an in vitro model simulating the physicochemical (pH, temperature and bile salts) and biological (gastric and pancreatic enzymes) gastrointestinal conditions. Some of the antioxidants in the kenaf seed extract were not relatively stable in the intestinal phase of the gastrointestinal tracts. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity and total phenolic content (TPC) assays displayed similar trends as the biostability of phenolic acids, which decreased during the digestion process. The overall percentage loss of selected phenolic acids was 8.4-49.4% in the intestinal phase. For the overall in vitro digestion system, significant correlations between phenolic acids, total phenolic content (TPC) and antioxidant activity (DPPH) were obtained in all digestion phases with the exception of the gastric phase.