Comparative study of phenolic content and antioxidant activity of strawberry puree,clear, and cloudy juices

The aim of this study was to determine the concentrations of phenolic compounds and their antioxidant activity in different kinds of juice: clear, cloudy, and puree which were made from three different strawberry cultivars (Elkat, Kent, and Senga Sengana). The anthocyanins, p-coumaric acid, ellagic acid, quercetin, keampferol derivatives, (+)-catechin, proanthocyanidins content and degree of proanthocyanidin polymerization, were determined both in the fresh and after 6 months of storage at 4 and 30 °C. Freshly produced juices contained higher amounts of phenolics, especially of anthocyanins and proanthocyanidins, than those stored for 6 months at 4 and 30 °C. The processing of the clear juice showed the higher loss of all phenolic compounds. The antioxidant capacity was the smallest for clear, and the highest for the puree juices. This was assessed by measurements made with different antioxidant activity assays: ABTS and FRAP. The puree of strawberry juice had significantly higher levels of the phenolic compounds and showed more antioxidant activity than the clear and cloudy juices, before and after storage in all strawberry cultivars.     

Comparison of six cultivars of strawberries (<Emphasis Type="Italic">Fragaria x ananassa</Emphasis> Duch.) grown in northwest Poland

The aim of this study was to compare the value of Senga Sengana, a long-term standard cultivar, with other cultivars grown in northwest Poland, namely Dukat, Elkat, Selva, Elsanta and Kent. The fruits were obtained from a commercial plantation and cultivated by applying conventional farming practice. Among the strawberry cultivars studied Elsanta berries had the highest vitamin C content and its leaves the highest ellagic acid content. Kent berries had the highest contents of total sugar, total polyphenol, total anthocyanin and ellagic acid derivatives. Dukat berries had the highest dry weight and soluble solids content. Senga Sengana berries had a slightly higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging effect than other cultivars. Consumer-objective colour measurements were performed to evaluate the quality of the fruit. Elsanta and Elkat berries were found to have the highest L (lightness), a^* (redness), C^* (chromaticity) and h (hue angle) values.     

Effect of l-ascorbic acid, sugar, pectin and freeze-thaw treatment on polyphenol content of frozen strawberries

The stability of phenolic compounds of three strawberry cultivars was evaluated for changes during prefreezing treatments, storage and various freezing and thawing conditions. Polyphenol content was determined by HPLC-DAD-FL. The sum of assayed polyphenolic (proanthocyanidin and monomeric flavan-3-ols, anthocyanins, ellagic acid, p-coumaric acid) represented 2858.4 mg/kg in Kent, 2893.1 mg/kg in Elkat, and 2438.0 mg/kg in Senga Sengana. After freezing, 4.5-33.6% of polyphenols were lost; protective effects of prefreezing treatments were seen on anthocyanidins and proanthocyanidins: ascorbic acid was the most effective pretreatment, allowing retention of 3.9-27.5% of anthocyanins, and almost total recovery (3.9-23.9%) when associated with liquid nitrogen freezing. Pectin and sugar only allowed retention of 3.0-25.1% and 5.5-25.4% of the antocyanins, respectively. Thawing of the strawberries in a microwave oven (instead of 20 h at 20 °C) had a further positive effect on retention of anthocyanins, proanthocyanins, (+)-catechin and ellagic acid.     

Quality characterisation of strawberries for industrial jam production

Six strawberry varieties were evaluated as raw materials for industrial jam production. The investigation involved chemical, physical and sensory analyses of fresh and frozen/thawed fruits as well as jam at the time of production and after 3 months of storage. Among the varieties studied, Jonsok and Senga Sengana appeared most suitable, followed by Bounty and Tenira. The other varieties, Fructana and Totem, were less satisfactory for this purpose. Based on linear correlation analyses (P<0.05), the relevance of various parameters in evaluating fruits intended for jam production is discussed. The results disclosed pH, titratable acids and sugars of fresh fruits to be less important to jam quality. High contents of soluble solids and ascorbic acid were related to undesirable flavour properties of jams. Further, high levels of ascorbic acid adversely affected colour stability. Colour degradation in jams was parallel to flavour deterioration. It is concluded that the main emphasis should be given to characteristics of the final products rather than to characteristics of the fresh fruits.     

Quantitative composition of volatile constituents in cultivated strawberries,Fragaria ananassa cv. senga sengana,senga litessa and senga gourmella

The volatile components of cultivated strawberries Fragaria ananassa cv. Senga Sengana, Senga Litessa and Senga Gourmella were studied by gas chromatography-mass spectrometry. Employing standard-controlled aroma separation by combined vacuum distillation-liquid-liquid extraction, as well as prefractionation on silica gel, the aroma substances of freshly harvested and deep-frozen strawberries from two growing seasons were quantitatively determined by gas chromatography. Methyl and ethyl butanoate, methyl and ethyl hexanoate, trans-2-hexenyl acetate, trans-2-hexenal, trans-2-hexen-1-ol as well as 2,5-dimethyl-4-methoxy-3(2H)-furanone were identified as main volatile components. In comparison to Senga Litessa and Senga Gourmella, Senga Sengana showed higher amounts of aroma compounds. In general, deep-freezing resulted in decreases of the concentrations of most of the aroma substances, but higher amounts of 2,5-dimethyl-4-methoxy-3(2H)-furanone were found in deep-frozen berries than in the freshly harvested ones.     

The effects of strawberry,black currant,and chokeberry extracts in a grain dietary fiber matrix on intestinal fermentation in rats

The objective of this work was to study the composition, hydration properties and oil holding capacity, antioxidant properties and the physiological effects on the digestive system of dietary preparations containing wheat or oat fiber enriched with polyphenol extracts from strawberry, chokeberry, and black currant pomace. By the addition of black currant, strawberry and chokeberry polyphenol extracts to grain fibers preparations with corresponding polyphenol content of 0.7%–0.8%, 1.1%–1.2%, and 2.5%–2.9% were obtained. The preparations were used as part (8%) of a modified AIN-93 diet given to growing Wistar rats (8 animals per group) over a period of 4 weeks. The highest antioxidant potential had grain–chokeberry preparations with the greatest polyphenol content, while grain–black currant preparations exhibited the lowest antioxidant potential with the smallest polyphenol content. The addition of strawberry and chokeberry extracts caused a decrease in the activity of bacterial β-glucosidase and α-galactosidase, while black currant extract led to increased activity of β-galactosidase and β-glucuronidase. The production of short chain fatty acids (SCFAs) in the caecum of rats fed the grain–strawberry preparation, rich in ellagitannins, was considerably higher than the grain–black currant preparation, rich in proanthocyanidins and anthocyans, or the grain–chokeberry preparation with the highest polyphenol content (78.3 vs. 64.7 vs. 56.3 μmol/100 g body weight, p = 0.012). In comparison to preparations without polyphenols only chokeberry extract significantly decreased SCFA concentration. The grain–strawberry preparations were characterized by a higher antioxidant potential per unit of polyphenol content and exhibited a more beneficial influence on the fermentation processes in the caecum of rats than the grain–black currant and grain–chokeberry preparations.     

Strawberry varieties for industrial jam production

Twelve strawberry varieties were investigated for potential use by the jam processing industry. Chemical, physical and sensory analyses were performed with fresh and thawed fruits and with jams made from the fruits. Fresh fruits were analysed for dry matter, soluble solids, pH, titratable acids and ascorbic acid. Total anthocyanin and degradation indexes were determined in both fresh fruits and in jams. Firmness of fresh and thawed fruits, as well as the amount of juice lost upon thawing (drip loss) were tested for each variety. Except for colour, no significant correlation (P<0.05) existed between the chemical analyses and the sensory parameters. There was significant relationship between total anthocyanin content and visual colour as judged by a taste panel. There was no correlation between firmness of fresh and thawed fruits. Drip loss and firmness of fresh fruits and jams gave a negative correlation. There was no relationship between drip loss and texture measurements in thawed fruits. Except for colour, there were no correlations between the chemical analyses. Based on the results, Jonsok, Totem and Bounty varieties appeared suitable for industrial jam production when compared to the Senga Sengana variety now in use.     

Ellagic acid content in berries: Influence of domestic processing and storage

The content of ellagic acid was determined from the berries of the family Rosaceae (strawberry, red raspberry, cloudberry, arctic bramble). Extraction and hydrolysis procedures were optimized and analysis was done with an HPLC method and UV detection. The influence of processing on ellagic acid content was studied in strawberry jam. Strawberries, red raspberries, and strawberry jam were analyzed fresh and after 3, 6, and 9 months of storage in a domestic freezer or refrigerator. Ellagic acid contents after 3 months of storage at −20 °C varied between 31.5 (strawberry ‘Senga Sengana’) and 68.6 mg/100 g f.w. (arctic bramble). Ellagic acid content in strawberry jam (23.8 mg/100 g f.w.) was 80% of that in unprocessed strawberries. The content of ellagic acid in strawberries and red raspberries was reduced by 40% and 30%, respectively, during the 9 months of storage at −20°C. The unprocessed berries studied, together with nuts, make the main contribution to the total dietary intake of ellagic acid in Finland. Received: 7 December 1999 / Revised version: 22 February 2000     

An evaluation of the retention of quality characteristics in fresh and freeze-dried alpine strawberries

Alpine strawberries (Fragaria vesca) are used in fruit juice, marmalade, or jam production and as a result have economical importance in food sector. The fresh alpine strawberries have a tendency to lose their quality in a few days as a result of high water loss and spoilage. In this paper, the results of a study on the effects of freeze drying process on the characteristics of the alpine strawberries, such as firmness, sugar content, pH, colour, weight loss, dissolved solids, anthocyanin and vitamin C content with reference to the fresh, are reported. Freeze‐drying indicated no difference in the characteristics of the alpine strawberries when compared with the fresh. It is found that a slight acid or base addition onto the rehydrated alpine strawberry juice preserved the stability of pigments and the colour. In addition, the rehydrated alpine strawberry juice exhibited an antimicrobial activity towards an important foodborne pathogen, Enterobacter faecium ATCC 6057.     

STORAGE STABILITY OF STRAWBERRY JAM COLOR ENHANCED WITH BLACK CARROT JUICE CONCENTRATE

Black carrot juice concentrate was added to enhance the color of strawberry jams prepared from two locally grown cultivars, Osmanl? and Kara. Compared to other cultivars processed to jams, these two cultivars are lightly colored but very aromatic. Color and pigment stability of colored and noncolored (control) strawberry jams were studied during storage. The use of black carrot concentrate as a source of natural colorant stabilized the color of strawberry jam. The stabilization was more noticeable for jams prepared from Osmanl? cultivar. Monomeric anthocyanin degradation was fitted to a first‐order reaction model. Storage temperature had a strong influence on anthocyanin degradation. As the storage temperature increased, the stability of anthocyanins decreased significantly in both colored and noncolored jams. Parallel to decrease in monomeric anthocyanins, hue (h°) values of all jam samples increased throughout the storage. However, increase in h° values was much smaller in colored samples than in noncolored samples. High correlation was found between h° value and anthocyanin concentration at 22C (r = 0.910–0.978) and 37C (r = 0.931–0.981).     

Rehydration and sorption properties of osmotically pretreated freeze-dried strawberries

The aim of this work was to investigate the influence of osmotic dehydration and type of osmotic solution on selected physical properties of freeze-dried strawberries. Frozen Senga Sengana strawberries were dehydrated in osmotic solution with water activity of about 0.9 (sucrose and glucose solutions and starch syrup). Osmotically dehydrated fruits were frozen and freeze-dried at heating shelf temperature of 30 °C for 24 h.     

Processing and storage effects on anthocyanin composition and antioxidant activity of jams produced with Camarosa strawberry

Anthocyanin profiles and radical scavenging activity of Camarosa strawberry jams as affected by two processing methods (conventional/industrial) and storage conditions were evaluated. Industrial strawberry jam produced in a closed system with vacuum preserved the anthocyanin composition (the total content was 35.77 ± 2.56 mg per 100 g) when compared with conventional jam produced in an open system (3.35 ± 0.05 mg per 100 g). However, the radical scavenging activity of conventional jam was lower than that of industrial jam, as EC₅₀ was 52.99 ± 0.94 and 44.33 ± 2.47 mg mL^?1, respectively. Two‐way analysis of variance indicated a significant effect of processing method and storage time during 60 days and a significant interaction for all variables except for EC₅₀. Long‐time storage of industrial jams at ?8 °C leads to 80% reduction in anthocyanin content without loss of sensorial characteristics, whereas at room temperature the reduction was 98%, and the red colour was replaced by a brownish. Regardless of storage temperature, the radical scavenging activity of jams decreased 50–60% of its initial value.     

Sugars and acids of strawberry varieties

The sugar and acid compositions of six strawberry (Fragaria×ananassa Duch.) varieties from 1997 and 1998, grown in different conditions, 26 samples in all, were investigated by GC as trimethylsilyl derivatives. The major sugars were glucose (1.89–4.52?g/100?ml), fructose (2.14–4.14?g/100?ml) and sucrose (0.90–3.87?g/100?ml), the major acids being citric (0.73–1.58?g/100?ml) and malic (0.22–0.69?g/100?ml). Total sugar content (glucose+fructose+sucrose) varied from 5.35?g/100?ml to 10.96?g/100?ml in accordance with soluble solids (°Brix). The correlation between them showed a linear regression y=0.873x-0.420, the percentage of determination of the regression model being 82.1%. Among one variety only, ‘Senga Sengana’, the percentage of the model was 86.9%. No significant differences were found between the strawberries from conventional versus those from organic farms. Contents of sugars and soluble solids were lower in varieties ‘Jonsok’ and ‘Honeoye’ than in ‘Korona’, ‘Bounty’ and ‘Polka’. The concentrations of malic acid were significantly higher in Senga Sengana, Jonsok and Bounty than in other varieties.     

Adding value to hard date (Phoenix dactylifera L.): Compositional,functional and sensory characteristics of date jam

Second-grade dates (with a hard texture) from three potential Tunisian cultivars (Deglet Nour, Allig and Kentichi) showed the same sugar (∼73.30–89.55 g/100 g dry matter), fibre (∼7.95–18.83 g/100 g dry matter) and total phenolics (∼280.6–681.8 mg of GAE/100 g) content as dates of high quality. Deglet Nour and Kentichi varieties were characterised by a high content of sucrose and low reducing sugar content; contrary to Allig and the majority of other date varieties tested. This work intended to add value to these raw materials by using them in jam production. The corresponding jams were characterised in terms of chemical composition, physical (texture and water retention capacities) and sensory properties. Results showed a significant effect of the date variety on the composition and physical characteristics of date jams. Indeed, Allig jam was richer in reducing sugars and was characterised by its higher firmness and water retention capacity. To test the acceptability of these new products, we compared them with quince jam (the most consumed in Tunisia). Results showed that Allig and Kentichi jams presented a higher overall acceptability. However, quince and Deglet Nour jams did not show any significant differences (P > 0.05). Results from this work revealed essential information that could promote the commercialization of dzate jam.     

An in vitro method to simulate phenolic compound release from the food matrix in the gastrointestinal tract

A method to simulate in vitro the physiological conditions in the stomach and small intestine has been developed as a modification of a method already described by Miller et al. [11]. This method enables the study of phenolic compound release from the food matrix and their transformation during digestion, and has been applied to orange juice, strawberries, and strawberry jam. The dialysis rates obtained for the different phenolics in the new method are much better than those found in the original one. Some food constituents, as is the case of sugars in jams, can affect the dialysis rates in vitro, showing that the results obtained for dialysis should be taken with caution in these products. These assays have shown that strawberry anthocyanins are largely degraded (transformed) during the digestion and that free ellagic acid is released from ellagitannins leading to a ten-fold increase of this compound during digestion.     

Determination of the fruit content of strawberry fruit preparations by gravimetric quantification of hemicellulose

A novel method for the determination of the fruit content of strawberry fruit preparations based on the quantification of hemicellulose is presented. For this purpose, the hemicellulose fraction was isolated from the alcohol-insoluble residue (AIR) of strawberry fruits (Fragaria × ananassa cv. ‘Senga Sengana’ and ‘Camarosa’) to calculate the amount of fresh fruit per gram hemicellulose. Fruit preparations with fruit contents ranging from 30% to 60% were produced using starch, pectin, xanthan and guar gum as hydrocolloids. For the determination of the fruit content, added hydrocolloids were removed by enzymatic digestion and alkaline degradation, respectively. The hemicellulose fraction resulting from AIR fractionation was quantified gravimetrically. Due to the characteristic composition of neutral sugars obtained after hydrolysis, the hemicellulose fractions may be used for authenticity control. Excellent agreement between specified and determined contents (30% vs. 31.5%; 45% vs. 44.7%; 60% vs. 64%; 40% vs. 37.6–42.2%) was obtained irrespective of the composition of the fruit preparation. This method is considerably more reliable than those based on the determination of low-molecular compounds which can easily be added to feign a higher fruit content. Furthermore, fruit juice concentrates added to fruit preparations as a food colorant do not affect the quantification of the fruit content.     

Degradation Kinetics of Anthocyanin of Traditional and Low-Sugar Blackberry Jam

The objective of this study was to monitor the stability of anthocyanin and phenolic compounds contained in two formulations of blackberry jam (traditional and low-sugar) during storage. For that purpose, jams were prepared with varying amounts of hydrocolloids and investigated as to pH, total soluble solids, water activity, total acidity, total anthocyanins and total polyphenols. In order to accompany and assess the levels of phenolic compounds and colour (L*, a* and b*) changes, the samples were stored for 180 days at two different temperatures (10 and 25 °C). The Arrhenius model was used to determine the relationship between the reaction rate (k) at the different storage temperatures, yielding activation energy values of 19 and 12 kcal/mol and Q ₁₀ values of 3.0 and 2.0 for traditional and low-sugar jams, respectively. The results show that by the end of the storage time investigated, the anthocyanin compounds had been partially degraded, with the greatest loss being observed in traditional jam stored at 25 °C. Colour stability was also lower in traditional jam as compared to the low-sugar product.     

Blood pressure-lowering properties of chokeberry (Aronia mitchurinii,var. Viking)

The blood pressure-lowering properties of lyophilized chokeberry juice and polyphenols were monitored using in vitro angiotensin-converting enzyme (ACE) inhibition measurement and a 10 day in vivo study with spontaneously hypertensive rats (SHR). Juice and polyphenols indicated weak ACE-inhibitory activity. The IC₅₀ values for polyphenols and juice were 1.5–2.5 and 4.5 mg dry matter/ml, respectively. In the SHR study the blood pressure-lowering effects of juice and polyphenol extract seemed to be short-term and were generally highest after 3 h from administration (50 mg/kg/day) when mean reductions in systolic blood pressure were 20 ± 8 and 15 ± 7 mm Hg, respectively. Corresponding mean decreases in diastolic blood pressure were 23 ± 6 and 13 ± 2 mm Hg in juice and polyphenol groups, respectively. It was concluded that both chokeberry juice and polyphenols had blood pressure-lowering effects. We hypothesize that chokeberry polyphenols enhance endothelial nitric oxide production with an ACE-independent mechanism, e.g. by activation of endothelial nitric oxidase enzyme; this is yet to be verified.     

Color quality of Oregon strawberries--impact of genotype, composition, and processing

ABSTRACT:  This investigation was to evaluate fruit color and study the effect of processing on color quality of strawberry products. Three color instruments with different viewing angles, viewing areas, and sample presentation geometries were compared for their effectiveness in measuring CIE L *C* h ^o color values for fresh fruits of 6 strawberry genotypes. There were significant differences between genotypes as well as between instruments. Fruits from the Totem genotype were frozen, canned, and made into jam. Color changes were measured along with the following compositional determinations: total monomeric anthocyanins (ACN), total phenolic content (TPC), and percent polymeric color. ACN in fresh strawberries ranged from 37.1mg to 122.3 mg per 100 g of fresh fruit. Freezing resulted in an apparent increase in ACN and transfer of 70.2% of the anthocyanins from the berries into juice. Physical transfer of pigments to syrup also occurred with canning: there was approximately 70% loss in ACN, about 20% increase in polymeric color, and 23.5% decrease in TPC. Pronounced color change and substantial losses in ACN and TPC of strawberry jams occurred during processing and 9 wk of storage. Storage of jams at 38 °C compared to 21 °C over a period of 9 wk resulted in marked losses of ACN and TPC.