Katherine Cools

Characterization of Industrial Onion Wastes (Allium cepa L.): Dietary Fibre and Bioactive Compounds

The food industry produces a large amount of onion wastes, making it necessary to search for possible ways for their utilization. One way could be to use these onion wastes as a natural source of high-value functional ingredients, since onion are rich in several groups of compounds, which have perceived benefits to human health. The objective of this work is to gain knowledge of any differences between the different onion wastes obtained from industry and non-commercial bulbs to use them as food ingredients rich in specific compounds. The results showed that brown skin and top–bottom could be potentially used as functional ingredient rich in dietary fibre, mainly in insoluble fraction, and in total phenolics and flavonoids, with high antioxidant activity. Moreover, brown skin showed a high concentration of quercetin aglycone and calcium, and top–bottom showed high concentration of minerals. Outer scales could be used as source of flavonols, with good antioxidant activity and content of dietary fibre. However, inner scales could be an interesting source of fructans and alk(en)yl cystein sulphoxides. In addition, discarded onions (cvs Recas and Figueres) could be used as a good source of dietary fibre, and cv Recas also as a source of phenolics compounds.

Ethylene and 1-Methylcyclopropene Differentially Regulate Gene Expression during Onion Sprout Suppression

Onion (Allium cepa) is regarded as a nonclimacteric vegetable. In onions, however, ethylene can suppress sprouting while the ethylene-binding inhibitor 1-methylcyclopropene (1-MCP) can also suppress sprout growth; yet, it is unknown how ethylene and 1-MCP elicit the same response. In this study, onions were treated with 10 μL L−1 ethylene or 1 μL L−1 1-MCP individually or in combination for 24 h at 20°C before or after curing (6 weeks) at 20°C or 28°C and then stored at 1°C. Following curing, a subset of these same onions was stored separately under continuous air or ethylene (10 μL L−1) at 1°C. Onions treated with ethylene and 1-MCP in combination after curing for 24 h had reduced sprout growth as compared with the control 25 weeks after harvest. Sprout growth following storage beyond 25 weeks was only reduced through continuous ethylene treatment. This observation was supported by a higher proportion of down-regulated genes characterized as being involved in photosynthesis, measured using a newly developed onion microarray. Physiological and biochemical data suggested that ethylene was being perceived in the presence of 1-MCP, since sprout growth was reduced in onions treated with 1-MCP and ethylene applied in combination but not when applied individually. A cluster of probes representing transcripts up-regulated by 1-MCP alone but down-regulated by ethylene alone or in the presence of 1-MCP support this suggestion. Ethylene and 1-MCP both down-regulated a probe tentatively annotated as an ethylene receptor as well as ethylene-insensitive 3, suggesting that both treatments down-regulate the perception and signaling events of ethylene.

Comparative study between extraction techniques and column separation for the quantification of sinigrin and total isothiocyanates in mustard seed

Glucosinolates are β-thioglycosides which are found naturally in Cruciferae including the genus Brassica. When enzymatically hydrolysed, glucosinolates yield isothiocyanates and give a pungent taste. Both glucosinolates and isothiocyanates have been linked with anticancer activity as well as antifungal and antibacterial properties and therefore the quantification of these compounds is scientifically important. A wide range of literature exists on glucosinolates, however the extraction and quantification procedures differ greatly resulting in discrepancies between studies. The aim of this study was therefore to compare the most popular extraction procedures to identify the most efficacious method and whether each extraction can also be used for the quantification of total isothiocyanates. Four extraction techniques were compared for the quantification of sinigrin from mustard cv. Centennial (Brassica juncea L.) seed; boiling water, boiling 50% (v/v) aqueous acetonitrile, boiling 100% methanol and 70% (v/v) aqueous methanol at 70 °C. Prior to injection into the HPLC, the extractions which involved solvents (acetonitrile or methanol) were freeze-dried and resuspended in water. To identify whether the same extract could be used to measure total isothiocyanates, a dichloromethane extraction was carried out on the sinigrin extracts. For the quantification of sinigrin alone, boiling 50% (v/v) acetonitrile was found to be the most efficacious extraction solvent of the four tested yielding 15% more sinigrin than the water extraction. However, the removal of the acetonitrile by freeze-drying had a negative impact on the isothiocyanate content. Quantification of both sinigrin and total isothiocyanates was possible when the sinigrin was extracted using boiling water. Two columns were compared for the quantification of sinigrin revealing the Zorbax Eclipse to be the best column using this particular method.

Effect of the transition between ethylene and air storage on post-harvest quality in six UK-grown potato cultivars

Summary Long-term storage of potato (Solanum tuberosum L.) tubers provides year-round availability of the crop, but is limited by sprouting. Continuous exposure to ethylene during storage can prolong the storage-life of potato tubers by suppressing sprouting, yet there is little information on the effects of ethylene on a wide selection of common cultivars. Six different UK potato cultivars were stored at 6ºC for 30 weeks under continuous 10 µl l 1 ethylene treatment, under continuous air, or transferred from air to 10 µl l 1 ethylene at the first indication of sprouting, or vice versa. Fructose, glucose, and sucrose concentrations were determined in samples of tuber flesh and in potato skins. Texture and sprouting were measured after 30 weeks in cold storage. Ethylene applied at the first indication of sprouting was as effective at suppressing further sprouting in ‘Desiree’, ‘Sylvana’, and ‘Fianna’ as observed when ethylene was applied continuously and resulted in no additional ethylene-induced sugar accumulation. The texture data suggested that ethylene treatment had an indirect effect on tuber firmness through the inhibition of sprout growth only in ‘Sylvana’ potato tubers. The implications of these results are that the cost of ethylene application in cold-store rooms could be reduced by manipulating the timing of its application.

Effect of UV-C on the physiology and biochemical profile of fresh Piper nigrum berries

Highlights • UV-C caused significant changes in colour (from green to brown).• A low UV-C dose significantly increased piperine and essential oil content.• A newly developed simultaneous extraction method is discussed.

CHAPTER 15:Extraction and Quantification of Sugars and Fructans from Vegetable Matter

Non-structural carbohydrates can be categorized into three main groups; monosaccharides, oligosaccharides and polysaccharides. The mono- and disaccharides; fructose, glucose and sucrose are found in a wide variety of vegetables including onions, green beans and potatoes. Fructans, which are long-chain carbohydrates, are found in very high concentrations in Jerusalem artichokes, onion, asparagus and globe artichokes. The measurement of sugar concentrations in vegetable matter is important for identifying changes in metabolism as a result of different developmental stages or pre- or post-harvest treatments and conditions. In addition, fructans and FOS have reported health promoting properties, therefore, vegetables with high concentrations are of nutritional interest. Extraction of sugars and fructans is relatively easy, although a wide variety of methods exist in the literature. Studies have shown methanol to be a superior solvent for sugar and fructan extraction although alkaline extraction procedures are often adopted when using high performance anion exchange chromatography with pulsed amperometric detector for compound separation and detection. Other techniques used to detect sugars and fructans include evaporative light scattering detector, refractive index detector and mass spectrometry. This chapter details methods used for the extraction, separation, identification and quantification of sugars and fructans in vegetable matter.

Spatial changes in leaf biochemical profile of two tea cultivars following cold storage under two different vapour pressure deficit (VPD) conditions

Highlights • Cold withering emphasised temporal changes in caffeine and theobromine content.• Spatial variations in catechin content observed between bud, large leaf and stem.• Vapour pressure deficit (VPD) conditions differentially affected caffeine levels.• Implications of mechanically harvested tea on final quality are discussed.

The effect of processing on the glucosinolate profile of mustard seed

Brassica juncea mustard seed are used to make mustard paste or condiment. Mustard seed contains glucosinolates which are converted to isothiocyanates following cell disruption by the enzyme, myrosinase. Isothiocyanates are sulphur-containing compounds which give a pungent flavour to the mustard condiment. Three mustard seed cultivars from two seasons were processed into Dijon- and wholegrain-style mustard and glucosinolates and isothiocyanates analysed. Canadian cv. Centennial tended to contain higher glucosinolates compared with the French cv. AZ147 and Ukrainian cv. Chorniava. Conversion of the mustard seed into a wholegrain condiment had a lesser effect on total isothiocyanates and sinigrin content compared with the Dijon-style preparation. The Canadian mustard cultivars produced wholegrain-style mustard with higher total isothyocyantes and sinigrin compared with the French and Ukrainian cultivars. In summary, results herein suggest that Canadian mustard seed cvs. Centennial and Forge, and wholegrain processing may result in a condiment with greater bioactive composition.