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PubMed1999

Effects of ozone treatment on postharvest strawberry quality.

The effect of ozone treatment on the postharvest quality of strawberry was evaluated. Strawberry fruits (Fragaria x ananassa Duch. cv. Camarosa) were stored at 2 degrees C in an atmosphere containing ozone (0.35 ppm). After 3 days at 2 degrees C, fruits were moved to 20 degrees C to mimic retail conditions (shelf life). The changes in several quality parameters such as fungal decay, color, sugar and acids distribution, and aroma were evaluated during the strawberries' shelf life. Ozone treatment was ineffective in preventing fungal decay in strawberries after 4 days at 20 degrees C. Significant differences in sugars and ascorbic acid content were found in ozone-treated strawberries. At the end of cold storage, the vitamin C content of ozonated strawberries was 3 times that of control fruits. A detrimental effect of ozone treatment on strawberry aroma was observed, with a 40% reduced emission of volatile esters in ozonated fruits.

Acetaldehyde↗
PubMed1998

Serum antioxidant capacity is increased by consumption of strawberries, spinach, red wine or vitamin C in elderly women.

It is often assumed that antioxidant nutrients contribute to the protection afforded by fruits, vegetables, and red wine against diseases of aging. However, the effect of fruit, vegetable and red wine consumption on the overall antioxidant status in human is unclear. In this study we investigated the responses in serum total antioxidant capacity following comsumption of strawberries (240 g), spinach (294 g), red wine (300 ml) or vitamin C (1250 mg) in eight elderly women. Total antioxidant capacity was determined using different methods: oxygen radical absorbance capacity (ORAC) assay, Trolox equivalent antioxidant capacity (TEAC) assay and ferric reducing ability (FRAP) assay. The results showed that the total antioxidant capacity of serum determined as ORAC, TEAC and FRAP, using the area under the curve, increased significantly by 7-25% during the 4-h period following consumption of red wine, strawberries, vitamin C or spinach. The total antioxidant capacity of urine determined as ORAC increased (P < 0.05) by 9.6, 27.5, and 44.9% for strawberries, spinach, and vitamin C, respectively, during the 24-h period following these treatments. The plasma vitamin C level after the strawberry drink, and the serum urate level after the strawberry and spinach treatments, also increased significantly. However, the increased vitamin C and urate levels could not fully account for the increased total antioxidant capacity in serum following the consumption of strawberries, spinach or red wine. We conclude that the consumption of strawberries, spinach or red wine, which are rich in antioxidant phenolic compounds, can increase the serum antioxidant capacity in humans. J. Nutr. 2383-2390, 1998

Aged↗
PubMed2003

Identification of a strawberry gene encoding a non-specific lipid transfer protein that responds to ABA, wounding and cold stress.

cDNA and genomic clones encoding a strawberry (Fragariaxananassa cv. Chandler) non-specific lipid transfer protein (Fxaltp gene) were isolated and characterized. The spatio-temporal expression pattern and structural features of this gene were studied for the first time in strawberry, a non-climacteric fruit of agricultural importance. The architecture and the encoded amino acid sequence of this non-climacteric fruit ltp gene were similar to those of other plant LTPs previously reported, and presents the eight cysteine residues and other features characteristic of plant LTPs. In addition, the deduced protein posseses an N-terminal signal peptide and lacks the K/HDEL retention signal, indicating that the strawberry LTP protein would enter the secretory pathway. In situ studies have shown that the Fxaltp gene is expressed in the epidermal cell layer of the strawberry fruit receptacle and achenes, flowers, and within the cell layer surrounding the endosperm. These results suggest that this Fxaltp gene promoter could be used as an endogenous promoter for biotechnological purposes in strawberry. Computer analysis using the PLACE database predicted the presence of several putative cis-regulatory sequences in response to abscisic acid and cold or wounding stresses within the Fxaltp 5'-flanking region. Accordingly, the strawberry gene responds to ABA and SA, but not to salt and heat stresses. It is also reported that ltp gene expression in strawberry is stimulated by wounding and repressed by cold stresses.

Abscisic Acid↗
PubMed1981

Demonstration of auxin binding to strawberry fruit membranes.

Presence of specific auxin-binding sites in strawberry fruit (Fragaria ananassa Duch. cv. Ozark Beauty) membranes has been demonstrated. These 1-naphthaleneacetic acid (NAA)-binding sites in the 80,000g to 120,000g fraction of the strawberry fruit membrane were pronase sensitive with an estimated equilibrium dissociation constant for NAA of 1.1 x 10(-6) molar. The minimum concentration of NAA required to stimulate strawberry fruit growth was at least one order of magnitude higher than the minimum concentration of NAA required to stimulate corn coleoptile elongation. This was consistent with the higher equilibrium dissociation constant (lower affinity) for auxin binding to strawberry fruit membranes than to corn coleoptiles. Twelve auxin analogs, ranging from very strong to weak auxins, were tested for abilities to stimulate in situ strawberry fruit growth and to bind (displace or compete with NAA) to strawberry fruit membranes. The observed positive correlation (r = 0.74) between the in vitro binding to the 80,000 to 120,000 membrane fraction and the in situ biological activity of these analogs indicated that the NAA-binding sites in strawberry fruit membranes may represent physiologically relevant auxin receptors.

Journal Article↗
PubMed2004

Bet v 1 homologues in strawberry identified as IgE-binding proteins and presumptive allergens.

BACKGROUND: No strawberry allergen has so far been identified and characterized. METHODS: Serum samples were collected from patients with a suggestive case history of adverse reactions to strawberry and other fruits. Extracts from fresh and frozen strawberries were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting and mass spectrometry. Patient blood samples were analysed for inhibition of IgE binding and basophil degranulation. RESULTS: Several IgE-binding proteins could be detected. In more than half of the patient sera, a 20/18-kDa doublet band was observed in Western blotting. These two bands were excised and analysed by mass spectrometry showing the presence of proteins belonging to the Bet v 1 family of allergens. Inhibition of the IgE binding to the 20/18-kDa doublet was obtained by addition of two recombinantly expressed allergens belonging to the Bet v 1 family (Bet v 1 and Mal d 1) and strawberry protein extract. In a cell-based assay of patient blood samples, basophil degranulation could be induced by strawberry protein extract and by Bet v 1 and Mal d 1. CONCLUSIONS: We conclude that strawberry homologues to Bet v 1 may be allergens of importance for adverse reactions to strawberry.

Adult↗
PubMed2001

Survival of Salmonella spp. and Escherichia coli O157:H7 on fresh and frozen strawberries.

For maximum shelf life, fresh strawberries are harvested directly without washing into retail containers. Frozen berries are usually hulled in the field and washed prior to freezing, sometimes with the addition of sucrose. To determine survival of potential bacterial contaminants, cut or intact surfaces of fresh strawberries were spot inoculated with five- or six-strain cocktails of Salmonella or Escherichia coli O157:H7 (log 7.0 CFU/sample). Inoculated strawberries were dried for 1 h at 24 degrees C and were stored in closed containers at 5 or 24 degrees C. Sliced strawberries with or without added 20% sucrose were inoculated with one of two strains of E. coli O157:H7 and frozen at -20 degrees C. An initial population reduction of approximately 0.5-log cycles was observed on intact but not cut berries after the 1-h drying period. During storage at 24 degrees C for up to 48 h, populations of Salmonella and E. coli O157:H7 did not decline further. When strawberries were stored at 5 degrees C for up to 7 days, populations of both pathogens remained constant on cut surfaces but decreased by 1 - to 2-log cycles on intact surfaces. After 30 days of frozen storage, the population of E. coli O157:H7 had declined by 0.7- to 2.2-log cycles (with and without sucrose, respectively). Results of this study indicate that E. coli O157:H7 and Salmonella are capable of survival but not growth on the surface of fresh strawberries throughout the expected shelf life of the fruit and can survive in frozen strawberries for periods of greater than 1 month.

Colony Count, Microbial↗
PubMed2005

Survival of Listeria monocytogenes on fresh and frozen strawberries.

Cut or intact surfaces of fresh strawberries were spot inoculated with a five-strain cocktail of nalidixic-acid resistant Listeria monocytogenes (10(6) (low inoculum) and 10(8) (high inoculum) CFU per three-berry sample). Inoculated strawberries were dried for 1 h at 24 degrees C and were stored in loosely closed containers at 4 or 24 degrees C. An initial population reduction of approximately 0.6 and 1.2 log cycles, high and low inoculum, respectively, was observed on intact but not cut berries after the 1-h drying period. A decrease of 1.4 and 3.3 log cycles per intact sample was observed over 48 h for the high and low inoculum, respectively, when stored at 24 degrees C. When held at 4 degrees C, a reduction of approximately 3 log cycles per intact-berry sample was observed for both inocula over the 7-day storage period. Populations on cut surfaces remained constant at both temperatures and both inoculum densities throughout the storage period. Sliced, inoculated strawberries (6.7 log CFU/25-g sample) with or without 20% sucrose were frozen at -20+/-2 degrees C. After 28 days of frozen storage, populations of L. monocytogenes determined on tryptose phosphate agar supplemented with nalidixic acid (TPAN) had declined by 0 to 1.2 log cycles, with and without 20% sucrose, respectively. Counts on modified Oxford agar supplemented with nalidixic acid were significantly (P< or =0.05) lower (0.5 to 1.8 log CFU/g) than on TPAN indicating that some cell injury had occurred. Results of this study indicate that L. monocytogenes is capable of survival but not growth on the surface of fresh intact or cut strawberries throughout the expected shelf life of the fresh fruit and can survive on frozen strawberries for periods of at least 4 weeks. On whole strawberries held at 24 degrees C, significantly faster declines (P< or =0.05) of L. monocytogenes were observed when lower rather than higher inoculum levels were applied.

Colony Count, Microbial↗
PubMed2001

Cytosolic aldolase is a ripening related enzyme in strawberry fruits (Fragaria x ananassa).

Two aldolase isoenzymes have been isolated from ripe strawberry fruits (Fragaria x ananassa cv. Camarosa and Elsanta) and partially purified by DEAE anion exchange and Sephacryl size exclusion chromatography. The isoenzymes were identified as class I cytosol and plastid aldolase on the basis of their chromatographic behavior on DEAE-cellulose columns, native molecular weight, pH optimum pattern, Km value for D-fructose-1,6-bisphosphate, tendency to be inactivated by lower pH values and SDS-PAGE subunit determination of 40 and 38 kDa, respectively. Total aldolase activity and distribution of both aldolase isoenzymes was also investigated at different stages of strawberry fruit ripening. Strawberries in the green and white ripening stage showed the same ratio of the two isoenzymes as green leaves with 15 and 8% cytosol aldolase activity, respectively. During strawberry fruit development the overall total aldolase activity decreased until the pink ripening stage and then increased due to a rise of cytosol aldolase yielding up to 75% in red strawberries. A cDNA putatively encoding the cytosolic form of aldolase in strawberry was cloned during the course of this study. Both microarray and RNA gel blot analyses showed that the cytosolic aldolase gene expression is induced during ripening as detected for the cytosolic aldolase enzyme. We suggest that induction of the cytosolic aldolase both at the levels of transcription and translation might be part of a ripening related stress response in the receptacle tissue.

Cloning, Molecular↗
PubMed2002

Inhibitory effect of whole strawberries, garlic juice or kale juice on endogenous formation of N-nitrosodimethylamine in humans.

In vitro and in vivo experiments were performed on inhibition of nitrosation by strawberry, garlic, and kale extracts. Strawberry, garlic, and kale extracts inhibited nitrosation in vitro. However, garlic extract has a greater ability to inhibit the chemical nitrosation in vitro than strawberry and kale extracts. The garlic methanol-soluble fraction of the garlic extract was fractionated into G1-G4 fractions by Prep-LC. Fraction G1 inhibited N-nitrosodimethylamine (NDMA) formation by 84+/-1%. We studied the formation of the carcinogen NDMA in humans after administration of nitrate (400 mg/day) in combination with an amine-rich diet and its possible inhibition by administration of whole strawberries (300 g), garlic juice (200 g: 75 g garlic juice in drinking water), or kale juice (200 g) in 27 males and 13 females (ten healthy volunteers in each group) of age 24+/-3 years. Nitrate intake resulted in a significant rise in mean salivary nitrate and nitrite concentrations. Also, nitrate excretion in urine during the experimental day was significantly increased compared with the control days. When whole strawberries, garlic juice, or kale juice was provided immediately after an amine-rich diet with a nitrate, NDMA excretion was decreased by 70, 71, and 44%, respectively, compared with NDMA excretion after ingestion of an amine-rich diet with a nitrate. These results suggest that consumption of whole strawberries, garlic juice, or kale juice can reduce endogenous NDMA formation.

Adolescent↗
PubMed2004

Genetic variation between Phytophthora cactorum isolates differing in their ability to cause crown rot in strawberry.

Analysis of 44 isolates of Phytophthora cactorum, isolated from strawberry and other hosts, by AFLP showed that the crown rot pathotype is different from leather rot isolates and from P. cactorum isolated from other hosts. 16 of 23 crown rot isolates, including isolates from Europe, Japan, Australia, and New Zealand, were identical in an analysis based on 96 polymorphic bands from seven primer combinations. Leather rot isolates of strawberry could not be distinguished from isolates from other hosts. The pathogenicity test of all 44 isolates on strawberry plants mostly gave unambiguous results, except for three American isolates, which seemed to have reduced aggressiveness compared to the crown rot isolates. These isolates also differed in the AFLP analysis. Comparing information on the origin of the isolates with results from the pathogenicity test, showed that isolates from strawberry fruits or petioles could be either leather rot or crown rot pathotypes. None of the isolates from hosts other than strawberry caused crown rot symptoms in strawberry.

DNA, Fungal↗
PubMed2001

Effect of plant growth temperature on antioxidant capacity in strawberry.

The influence of four day/night growing temperature combinations (18/12, 25/12, 25/22, and 30/22 degrees C) on phenolic acid, flavonol, and anthocyanin content and their antioxidant activities against peroxyl radicals (ROO(*)), superoxide radicals (O(2)(*)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radicals (OH(*)), and singlet oxygen ((1)O(2)) in fruit juice of Earliglow and Kent strawberry (Fragaria x ananassa Duch.) cultivars was studied. Pelargonidin-based anthocyanins such as pelargonidin 3-glucoside (291.3-945.1 microg/g fresh wt.), pelargonidin 3-rutinoside (24.7-50.9 microg/g fresh wt.), and pelargonidin 3-glucoside-succinate (62.2-244.0 microg/g fresh wt.) were the predominant anthocyanins in strawberry fruit juice. The content of cyanidin-based anthocyanins, cyanidin 3-glucoside and cyanidin 3-glucoside-succinate, was much lower than that of pelargonidin-based anthocyanins. Strawberry growth in high temperature conditions significantly enhanced the content of p-coumaroylglucose, dihydroflavonol, quercetin 3-glucoside, quercetin 3-glucuronide, kaempferol 3-glucoside, kaempferol 3-glucuronide, cyanidin 3-glucoside, pelargonidin 3-glucoside, pelargonidin 3-rutinoside, cyanidin 3-glucoside-succinate, and pelargonidin 3-glucoside-succinate in strawberry juice. Plants grown in the cool day and cool night temperature (18/12 degrees C) generally had the lowest phenolic acid, flavonols, and anthocyanins. An increase in night temperature from 12 to 22 degrees C, with the day temperature kept constant at 25 degrees C, resulted in a significant increase in phenolic acid, flavonols, and anthocyanins. These conditions also resulted in a significant increase in antioxidant capacity. The highest day/night temperature (30/22 degrees C) yielded fruit with the most phenolic content as well as ROO(*), O(2)(*)(-), H(2)O(2), OH(*), and (1)O(2) radical absorbance capacity. Fruit of Kent cv. strawberry had higher values of phenolic acid, flavonols, anthocyanins, and antioxidant capacities than fruit of Earliglow cv. strawberry under all temperature regimes.

Anthocyanins↗
PubMed2002

Volatile compounds of selected strawberry varieties analyzed by purge-and-trap headspace GC-MS.

Six strawberry (Fragaria x ananassa Duch.) varieties, Senga Sengana, Jonsok, Polka, Korona, Bounty, and Honeoye, were studied in relation to composition of their volatile headspace compounds collected by dynamic purge-and-trap concentration. Also, the influence of cultivation technique on the volatile compounds was tested by comparing conventionally and organically cultivated strawberry varieties. In addition, the effect of geographical origin on strawberry volatiles was investigated. The emphasis of this study was lay in the industrial utilization of strawberry. A total of 52 different volatile compounds were determined from frozen strawberries grown in 1997 and 1998. In addition to individual compounds, total areas of chromatogram profiles were compared. The major esters were found to be methyl butanoate, ethyl butanoate, methyl hexanoate, and ethyl hexanoate. With the application of principal component analysis and analysis of variance to the data matrix, the varieties were classified into three groups. Var. Honeoye was most different from the others. Organic cultivation had no effect on strawberry volatiles.

Crosses, Genetic↗
PubMed2002

Biosynthesis of strawberry aroma compounds through amino acid metabolism.

The fate of amino acids in relation to aroma biogenesis was studied in strawberries using the in vitro growth approach. This fruit presented differences in the level of metabolization for different amino acids. Incubations of strawberries with L-isoleucine gave rise to an increase of fourteen compounds in this fruit aroma, either not detected previously or constituents of strawberry aroma. However, L-valine incubations did not provide a significant change in this fruit aroma. Strawberry feeding with L-isoleucine resulted in a 7-fold increase in the sum of 2-methylbutanoate esters, and a double production of 2-methylbutyl esters compared to those of control fruits. Around 94% of the ester increase corresponded to 2-methylbutanoates, with ethyl 2-methylbutanoate being the most representative compound (92%). On the other hand, among the 2-methylbutyl esters, comprising around 6% of total aroma volatiles increase, 2-methylbutyl acetate was the major compound (95%) arising from L-isoleucine strawberry feeding. The role of enzymatic activities within the amino acid metabolic pathway in strawberry fruits is discussed.

Acyltransferases↗
PubMed1999

H(2)O(2)-mediated pigment decay in strawberry as a model system for studying color alterations in processed plant foods.

Phenolic and pigment (anthocyanin) stability in processing-ripe strawberries in response to aging under mildly oxidizing conditions, provoked by exogenous application of H(2)O(2), has been studied to design a simplified model system to study color alterations (pigment decay) that occur in strawberry-derived foods during processing and storage. The results showed that phenolic metabolism in strawberry slices during aging under mildly oxidizing conditions may be either oxidative (independent of exogenous H(2)O(2)) or peroxidative (dependent on exogenous H(2)O(2)), and that feeding strawberry slices with H(2)O(2) stimulates the oxidative phenomena which take place in their absence, such as the processes of anthocyanin and catechin degradation. The results also showed that because both (+)-catechin and anthocyanin levels in strawberry slices fall as H(2)O(2) increases, both p-hydroxybenzoic acid and brown polymeric compounds are formed. Comparison of these results with controls in the absence of H(2)O(2) suggests that peroxidase may play an important role in catechin consumption and in anthocyanin degradation and brown polymer formation during the aging of strawberry slices under mildly oxidizing conditions.

Color↗
PubMed1999

Lipoxygenase and hydroperoxide lyase activities in ripening strawberry fruits.

The enzymes lipoxygenase and hydroperoxide lyase have been identified in strawberry (Fragariax ananassa Duch.) var. Camarosa. Their subcellular localization, substrate preference, and product specificity were determined in mature strawberry fruits. The activity of both enzymes was located mainly in the microsomal fraction. Linolenic acid was the preferred substrate for strawberry lipoxygenase, forming 13- and 9-hydroperoxides of this acid in the proportion 70:30. The strawberry hydroperoxide lyase cleaves 13-hydroperoxide of linoleic (13% relative activity) and linolenic (100% relative activity) acids to form hexanal and (3Z)-hexenal, respectively. Both enzyme activities and endogenous content of volatile aldehydes formed by sequential action of lipoxygenase-hydroperoxide lyase were evaluated during strawberry development and ripening. A sequential enzymatic pathway for the formation of green odor compounds in strawberry is proposed.

Aldehyde-Lyases↗
PubMed1997

Cloning, molecular characterization and expression pattern of a strawberry ripening-specific cDNA with sequence homology to pectate lyase from higher plants.

A strawberry fruit cDNA showing sequence similarity to higher-plant pectate lyase genes has been isolated by differential screening of a strawberry fruit cDNA subtractive library. The cDNA contains a 396 amino acids open reading frame corresponding to a 44.8 kDa protein. The transcript is predominantly expressed in ripe fruits and was not detected at high levels in any other plant tissues. The removal of the achenes from unripe green fruits induced the expression of this putative pectate lyase gene. In common with other ripening related genes in strawberry, this induction was partially inhibited by treatment of de-achened fruit with the auxin NAA. Southern blot analysis of genomic DNA indicates that in strawberry there is more than one putative pectate lyase gene. We propose that the ripe fruit expression of this strawberry gene with similarity to pectate lyases could be related to cell wall pectin degradation contributing to strawberry fruit softening.

Amino Acid Sequence↗
PubMed2002

Cloning, expression and immunolocalization pattern of a cinnamyl alcohol dehydrogenase gene from strawberry (Fragaria x ananassa cv. Chandler).

Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the conversion of p-hydroxy-cinnamaldehydes to the corresponding alcohols and is considered a key enzyme in lignin biosynthesis. By a differential screening of a strawberry (Fragariax ananassa cv. Chandler) fruit specific subtractive cDNA library, a full-length clone corresponding to a cad gene was isolated (Fxacad1). Northern blot and quantitative real time PCR studies indicated that the strawberry Fxacad1 gene is expressed in fruits, runners, leaves, and flowers but not in roots. In addition, the gene presented a differential expression in fruits along the ripening process. Moreover, by screening of a strawberry genomic library a cad gene was isolated (Fxacad2). Similar to that found in other cad genes from higher plants, this strawberry cad gene is structured in five exons and four introns. Southern blot analyses suggest that, probably, a small cad gene family exists in strawberry. RT-PCR studies indicated that only the Fxacad1 gene was expressed in all the fruit ripening stages and vegetative tissues analysed. The Fxacad1 cDNA was expressed in E. coli cells and the corresponding protein was used to raise antibodies against the strawberry CAD polypeptide. The antibodies obtained were used for immunolocalization studies. The results showed that the CAD polypeptide was localized in lignifying cells of all the tissues examined (achenes, fruit receptacles, runners, leaves, pedicels, and flowers). Additionally, the cDNA was also expressed in yeast (Pichia pastoris) as an extracellular protein. The recombinant protein showed activity with the characteristic substrates of CAD enzymes from angiosperms, indicating that the gene cloned corresponds to a CAD protein.

Alcohol Oxidoreductases↗
PubMed2005

Different ethylene receptors show an increased expression during the ripening of strawberries: does such an increment imply a role for ethylene in the ripening of these non-climacteric fruits?

Notwithstanding the economic importance of non-climacteric fruits like grape and strawberry, little is known about the mechanisms that regulate their ripening. Up to now no growth regulator has emerged with a primary role similar to that played by ethylene in the ripening of the climacteric fruits. Strawberries can produce ethylene, although in limited amounts. Two cDNAs coding for enzymes of the ethylene biosynthetic pathway (i.e. FaACO1 and FaACO2), and three cDNAs encoding different ethylene receptors have been isolated. Two receptors (i.e. FaEtr1 and FaErs1) belong to the type-I while the third (i.e. FaEtr2) belongs to the type-II group. The expression of both the ACO and the receptor-encoding genes has been studied in fruits at different stages of development and in fruits treated with hormones (i.e. ethylene and the auxin analogue NAA). All the data thus obtained have been correlated to the known data about ethylene production by strawberry fruits. Interestingly, a good correlation has resulted between the expression of the genes described in this work and the data of ethylene production. In particular, similarly to what occurs during climacteric fruit ripening, there is an increased synthesis of receptors concomitant with the increased synthesis of ethylene in strawberries as well. Moreover, the receptors mostly expressed in ripening strawberries are the type-II ones, that is those with a degenerate histidine-kinase domain. Since the latter domain is thought to establish a weaker link to the CTR1 proteins, even the little ethylene produced by ripening strawberries might be sufficient to trigger ripening-related physiological responses.

Amino Acid Oxidoreductases↗