1 Chair of Microbiology, Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000 Ljubljana, Slovenia
2 Chair for Microbiology and Biotechnology, ...Department of Animal Science, Biotechnical Faculty, University of Ljubljana, Groblje 3, 1230 Domzale, Slovenia
The membrane fatty acid composition of Escherichia coli becomes conditioned during periodic temperature cycling between 37 and 8 °C. After several cycles of temperature change, the bacteria become locked into a low-temperature physiology. Even after a prolonged incubation at high temperature the membrane fatty acid composition of conditioned cells was similar to that of cold-stressed cells.
Correspondence David Stopar david.stopar{at}bf.uni-lj.si
Abbreviations: ; C16 : 1, palmitoleic acid; C17 : 0cyc, methylene hexadecanoic acid; C18 : 1, cis -vaccenic acid; SFA, saturated fatty acid; UFA, unsaturated fatty acid
Size and weight are one of the most important quality factors of strawberries along with color and taste. Based on these factors, the fruit can be marked as non-marketable as fresh fruit and culled ...or used for further processing, even though it provides a desirable taste and colour. In this study, differences in composition among fruit of different sizes and weights within two strawberry cultivars (‘Lycia’ and ‘Clery’) were evaluated (physical parameters, TSS, organic acids, sugars, anthocyanins, and other phenolic compounds). Ascorbic acid and sugar content (per fresh weight) were higher in larger fruit for both studied cultivars. In 'Lycia', the large fruit contained on average 20% more sugars and 35% more ascorbic acid. The small fruit showed higher anthocyanin content than the large fruit by 245 and 63.4 mg kg− 1 for 'Clery' and 'Lycia', respectively. However, the total organic acids content and peroxidase and polyphenol oxidase activity did not show any differences among the fruit of different sizes. Small-sized fruit can serve as a good source of antioxidants due to the high anthocyanin content and can be suitable for further processing due to the lower ascorbic acid content and higher anthocyanin content.
•Strawberries show differences in composition depending on their size.•Large strawberry fruit contains more sugars and ascorbic acid.•Small-sized strawberries show higher content of anthocyanins.•Small-sized strawberries seem to be more suitable for further processing.
Strawberries are appreciated by consumers for their characteristic taste and health benefits, which enhance their demand throughout the year. Everbearing strawberries can produce fruits for a longer ...period and could thus meet this demand, but the fruit quality depends on environmental factors and the cultivar. This study focused on the effect of environmental conditions on the physical attributes and the composition of everbearing Capri cultivar fruit harvested from the end of June to the end of October. A positive correlation was observed between temperature and organic acid content (r = 0.87), and a positive correlation was observed between sunshine duration, anthocyanin (r = 0.87) and phenolic compound contents (r = 0.89). Additionally, the composition of sugars was affected by the environmental conditions. While strawberries harvested towards the end of October, when lower temperatures predominated, were larger in size and had a higher sugar/acid ratio, fruit harvested in the middle of August, when there were longer periods of sunshine, had higher anthocyanin and phenolic compound contents. In conclusion, strawberries with higher sugar/acid ratios are obtained when temperatures are lower, while strawberries exposed to longer periods of sunshine are richer in health-promoting compounds.
Secondary metabolites, namely, phenolic and volatile organic compounds, contribute to the nutritional and organoleptic quality of the strawberry fruit. This study focuses on the changes in the ...content of phenolic compounds and volatile organic compounds during the ripening, from green to overripe fruit, of five strawberry cultivars ('Asia', 'CIVN 766', 'Aprica', 'Clery', and 'Malwina'). Additionally, these changes are compared with the colour of the fruit and peroxidase and polyphenol oxidase activity. Our results show that the accumulation of secondary metabolites (phenolic and volatile organic compounds) significantly changed during the ripening process for all of the studied cultivars. As for phenolic compounds, flavanols and hydroxybenzoic acid derivatives comprised between 87 and 95% of the total phenolic compound content in unripe green fruit. In contrast, anthocyanins and hydroxycinnamic acid derivatives comprised between 64 and 77% of the total phenolic compound content in overripe fruit, except in the fruit of the cultivar 'CIVN766'. When it comes to the aroma profile, the content of aldehydes decreased by 24-49% as the fruit ripened, and the accumulation of esters increased. Our study also shows that the ripening process differs among cultivars, and it is therefore necessary to define ripening indicators separately for each cultivar.
The distribution of primary and secondary metabolites within a fruit can affect its nutritional and organoleptic quality, as fruit can vary in size and shape. This study investigated the differences ...in the distribution of the primary and secondary metabolites in the fruit of four strawberry cultivars (‘Asia’, ‘Clery’, ‘Frederica’, and ‘Sandra’) that were collected at one harvest point. The study included an analysis of the individual sugars, organic acids, phenolic compounds, and enzymes responsible for the degradation of phenolics. All of the studied cultivars showed a lower pH, higher total organic acid content, and lower glucose and fructose content in the outer part of the fruit. Differences were also observed in the total phenolic and anthocyanin contents, which were always higher in the outer part. The absolute differences in the total phenolic content ranged from 3723 to 6154 mg kg−1 dry weight. Our results provide a basis for understanding the differences in the biosynthesis of these metabolites within this fruit and prove that it is essential to mix samples well before extractions to obtain results that are representative of the whole fruit.
The importance of bacterial, phytoplankton and dissolved alkaline phosphatase activity (APA) in the northern Adriatic was investigated during 2006. In surface waters total APA increased from early ...spring (0.07–0.08
μmol
l
−1
h
−1) to late spring (up to 4.64
μmol
l
−1
h
−1) and remained relatively high during the summer (0.46–0.71
μmol
l
−1
h
−1), due to an increase in specific phytoplankton (up to 30
nmol
μg
C
−1
h
−1) and bacterial APA (up to 17.11
nmol
μg
C
−1
h
−1). Activity of free enzymes was not important. During late spring and summer both communities exploited dissolved organic phosphorus although, taking into account biomass, phytoplankton activity usually dominated over bacterial activity. In autumn an extra P supply from deeper waters drastically reduced phytoplankton APA, though not bacterial APA, in upper waters. Probably in these months bacteria that were degrading phytoplankton produced organic matter were P limited. In deeper waters APA was low and mainly due to the activity of free enzymes.
Differentiation of the plankton food web structure was studied during the 2003–2008 period, in situations when the system of the northern Adriatic Sea, one of the most productive area in the ...Mediterranean, switched from low nutrient to higher nutrient regime. The biomass distribution between autotrophs, bacteria, protozoans and metazoans showed that within the upper part of the water column the microbial food web was developed during the stratification period (May–September) in oligotrophic conditions, with a larger heterotrophic/autotrophic (H/A) ratio in the western (1.4–1.7) than in the eastern part (1.2–1.5). Classical food web patterns (H/A 0.3–0.7) were observed when additional nutrient supply by freshwater (stratification period) or/and by mixing throughout the water column (November–March) occurred. However, while the stratification period with freshets (originated from the Po River outflow) was characterized by an increased biomass of autotrophs and heterotrophs, there was a reduction of biomasses during the mixing period, indicating increased carbon export from the area. In the bottom layer heterotrophs were not able to use the excess of autotrophic production, hence probably a part of autotrophs sank to the sediments fuelling benthic communities. Moreover, recurrently higher metazoans than protozoans biomass ratios suggested the occurrence of herbivorous and microbial grazing modes of metazoans.
► Changes in food web structure occurred in different nutrients regime. ► In upper waters microbial food web develops during oligotrophic conditions. ► Classical food web was found during the enhanced nutrient level induced by freshwater input or water column mixing. ► Multivorous food web was observed in lower waters.
During the 1990–2008 period heterotrophic prokaryotes abundance (HP) in the northern Adriatic showed a substantial decrease after 2003. Before 2003 the HP annual cycle was characterized by minimal ...values during winter (100–134
·
10
7
cell
l
−
1
, on average) and a gradual increase toward summer (up to 212
·
10
7
cell
l
−
1
, on average). After 2003 HP was low during the most part of the year (27–63
·
10
7
cell
l
−
1
, on average), with somewhat higher values only at the end of summer and in April (up to 80
·
10
7
cell
l
−
1
in average). The overall higher Leu/TdR ratio after 2003 showed that prokaryotes were increasing their cellular biomass but more slowly dividing than before. There were indications that changed hydrographic conditions, reduced substrate supply and quality changes might be the most responsible factors for the observed HP decrease and change in their growth characteristics. As a consequence of lower HP heterotrophic flagellates abundance (HF) after 2003 (average 0.57
·
10
6
cell
l
−
1
) generally decreased by about three times. Weakened coupling between HP and HF confirmed the minor role of grazing pressure in controlling HP after 2003. This study shows the direct response of the microbial community to meteorological and subsequent hydrographical condition changes that occurred in the northern Adriatic.
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