Impacts of depectinization of pear juice on alcoholic fermentation and indole formation

BACKGROUND

Recently, a producer of fermented ciders observed 'vinyl' off-odors formed during fermentation of pear juice previously depectinized at ≥ 49 °C but not if depectinized at lower temperatures. The objective of this study was to investigate the source of this spoilage and evaluate factors that affect formation.

RESULTS

Analysis of untainted and tainted samples obtained from the producer determined the causative agent to be indole, a compound sometimes produced by yeast (Saccharomyces cerevisiae) during fermentation. To mimic commercial depectinization conditions, pectinases were added to pear juices held at 35 °C for 45 min (Treatment A), 49 °C for 45 min (Treatment B), or 49 °C for 90 min (Treatment C). Juice processing conditions did not affect yeast growth nor progress of alcoholic fermentation. Although neither yeast strain (DV10 or MERIT) synthesized indole during fermentation of Treatment A juices, the compound was produced by MERIT in Treatments B (27.05 μg L^-1 ) and C (469.9 μg L^-1 ). Supplementation of Treatment C juice with pyridoxine (vitamin B₆ ) prior to fermentation resulted in no detectable indole formed. However, juices from Treatments A, B, or C contained similar concentrations of pyridoxine and non-detectable amounts of tryptophan, a potential precursor to indole. Furthermore, indole was not detected during fermentations of a synthetic pear juice medium without pyridoxine.

CONCLUSION

Supplementation of cider musts with pyridoxine prior to fermentation and choice of yeast strain can lower the risk of formation of off-odors caused by indole. However, other unidentified factors are present which affect its formation in perry. © 2019 Society of Chemical Industry.

'Scarlett Spur Red Delicious' apple volatile production accompanying physiological disorder development during low pO2 controlled atmosphere storage

Apple (Malus domestica Borkh.) fruit volatile production is regulated by a variety of factors including low oxygen storage conditions. This study examined the impact of low pO2 controlled atmospheres on 'Scarlett Spur Red Delicious' apple volatile production and disorder development. Accumulation of apple volatile compounds was characterized during long-term cold storage at 0.5 °C in air or low pO2 (0.3, 0.8, or 1.5 kPa) with 1 kPa CO2. Volatile accumulation differed quantitatively with pO2 as acetaldehyde, ethanol, and ethyl ester accumulation increased with decreased pO2 during the first weeks in storage. Differences in volatile accumulation among atmospheres were evident through 6 months. The rate of ethanol accumulation increased with decreased pO2 and could potentially be used to monitor low O2 stress. Incidence of low oxygen disorders after 9 months was highest in fruit held at the lowest pO2. The sesquiterpene α-farnesene was not detected throughout the storage period.

Effects of Enhanced UV-B Radiation on Plant Chemistry: Nutritional Consequences for a Specialist and Generalist Lagomorph

Ultraviolet-B (UV-B) radiation has been increasing in temperate latitudes in recent decades and is expected to continue rising for some time. Enhanced UV-B radiation can change plant chemistry, yet the effects of these changes on mammalian herbivores are unknown. To examine the influence of enhanced UV-B radiation on nutrition of a specialist and generalist hindgut fermenter, we measured nutritional and chemical constituents of three common North American range plants, big sagebrush (Artemisia tridentata), yarrow (Achillea millefolium), and bluebunch wheatgrass (Pseudoregneria spicata), and how these changes influenced in vitro dry matter digestibility and in vivo digestibility by pygmy rabbits (Brachylagus idahoensis) and eastern cottontails (Sylvilagus floridanus). Forages were irradiated for 3 mo with ambient (1x) or supplemental (1.6x) UV-B radiation representing a 15% ozone depletion for Pullman, WA, USA. Enhanced UV-B radiation had minimal effects on the nutritional content and the tannin-binding capacity of forages. Similarly, the terpene concentration in sagebrush and yarrow was not affected by higher UV-B irradiances. Flavonoid compounds increased in sagebrush but decreased in yarrow. Rabbit preference and intake was not affected by treatment levels for any forage species and no differences were found between treatments for dry matter, fiber, protein digestibility, and apparent digestible energy.

The influence of nitrogen and biotin interactions on the performance of Saccharomyces in alcoholic fermentations

AIM

To study the impact of assimilable nitrogen, biotin and their interaction on growth, fermentation rate and volatile formation by Saccharomyces.

METHODS AND RESULTS

Fermentations of synthetic grape juice media were conducted in a factorial design with yeast assimilable nitrogen (YAN) (60 or 250 mg l(-1)) and biotin (0, 1 or 10 microg l(-1)) as variables. All media contained 240 g l(-1) glucose + fructose (1 : 1) and were fermented using biotin-depleted Saccharomyces cerevisiae strains EC1118 or UCD 522. Both strains exhibited weak growth and sluggish fermentation rates without biotin. Increased nitrogen concentration resulted in higher maximum fermentation rates, while adjusting biotin from 1 to 10 microg l(-1) had no effect. Nitrogen x biotin interactions influenced fermentation time, production of higher alcohols and hydrogen sulfide (H(2)S). Maximum H(2)S production occurred in the medium containing 60 mg l(-1) YAN and 1 microg l(-1) biotin.

CONCLUSIONS

Nitrogen x biotin interactions affect fermentation time and volatile production by Saccharomyces depending on strain. Biotin concentrations sufficient to complete fermentation may affect the organoleptic impact of wine.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the necessity to consider nutrient interactions when diagnosing problem fermentations.

Influence of ethylene action, storage atmosphere, and storage duration on diphenylamine and diphenylamine derivative content of Granny Smith apple peel

The application of diphenylamine (DPA) to prevent the apple peel disorder superficial scald can result in accumulation of a number of DPA derivatives resulting from C-nitration, C-hydroxylation, O-methylation, and N-nitrosation during fruit storage. As the presence of these compounds may be indicative of metabolic processes leading to superficial scald development, the contents of DPA and DPA derivatives were determined in fruits treated at harvest with DPA or DPA plus the ethylene action inhibitor 1-methylcyclopropene (1-MCP), which also prevents scald development. Influences of fruit maturity, storage environment, storage duration, and a 14 day poststorage ripening period on accumulation of DPA metabolites were also assessed. Poststorage ripening, 1-MCP treatment, and controlled atmosphere storage had varied effects on DPA derivative contents suggesting that reactive oxygen and nitrogen species, such as *OH, *NO, and *NO2, or enzyme-catalyzed reactions may be present during certain ripening and senescence-related physiological processes. Definitive correlations between superficial scald incidence and contents of specific derivatives were not observed.

Relationship of superficial scald development and alpha-farnesene oxidation to reactions of diphenylamine and diphenylamine derivatives in Cv. Granny Smith apple peel

Cv. Granny Smith apple fruit, treated at harvest with aqueous emulsions containing diphenylamine (DPA) and DPA derivatives, were evaluated for the peel disorder superficial scald (scald) after 6 months of cold storage at 1 degrees C plus 0 or 7 days at 20 degrees C. Metabolism of these derivatives and alpha-farnesene oxidation were also evaluated after 6 months. Derivatives substituted at the para position prevented scald, but scald developed on fruit treated with derivatives substituted in the amino, ortho, or meta positions. The extent of scald control was also dependent on the chemical nature of the functional group used to derivatize DPA. Hydroxylation of DPA and DPA derivatives during storage was not associated with scald control. Methoxylated DPA derivatives produced during storage resulted from O-methylation of C-hydroxylated derivatives rather than C-methoxylation of DPA. N-Nitrosodiphenylamine provided partial scald control, possibly resulting from its degradation to DPA, indicating that the amino hydrogen of DPA may be crucial for scald control. Results suggest that functional group position and chemical properties both contribute to the efficacy of DPA derivatives for scald control.

Analysis of volatile compounds from various types of barley cultivars

We identified volatile compounds of barley flour and determined the variation in volatile compound profiles among different types and varieties of barley. Volatile compounds of 12 barley and two wheat cultivars were analyzed using solid phase microextraction (SPME) and gas chromatography. Twenty-six volatiles comprising aldehydes, ketones, alcohols, and a furan were identified in barley. 1-Octen-3-ol, 3-methylbutanal, 2-methylbutanal, hexanal, 2-hexenal, 2-heptenal, 2-nonenal, and decanal were identified as key odorants in barley as their concentration exceeded their odor detection threshold in water. Hexanal (46-1269 microg/L) and 1-pentanol (798-1811 microg/L) were the major volatile compounds in barley cultivars. In wheat, 1-pentanol (723-748 microg/L) was a major volatile. Hulled barley had higher total volatile, aldehyde, ketone, alcohol, and furan contents than hulless barley, highlighting the importance of the husk in barley grain aroma. The proanthocyanidin-free varieties generally showed higher total volatile and aldehyde contents than wild-type varieties, potentially due to decreased antioxidant activity by the absence of proanthocyanidins.

Evaluation of diphenylamine derivatives in apple peel using gradient reversed-phase liquid chromatography with ultraviolet–visible absorption and atmospheric pressure chemical ionization mass selective detection

A method was developed for extracting, identifying, and quantifying diphenylamine (DPA) derivatives in the peel of DPA-treated apples using gradient reversed-phase liquid chromatography with ultraviolet-visible absorption and atmospheric pressure chemical ionization detection (LC-UV-vis-APCI-MS). Compounds routinely analyzed using this method included hydroxylated, nitrosated, nitrated, and methoxylated diphenylamine derivatives. Analysis of peel treated with 0-8 g L(-1) DPA showed that peel DPA content was a limiting factor in derivative production and that recovery of most compounds over this range was linear.

Ultraviolet-B radiation alters phenolic salicylate and flavonoid composition of Populus trichocarpa leaves

We investigated foliar phenolic composition of field- and greenhouse-grown Populus trichocarpa Torr. & A. Gray (black cottonwood) ramets subjected to near zero (0x), ambient (1x) or twice ambient (2x) concentrations of biologically effective ultraviolet-B (UV-B) radiation. After a 3-month treatment period, several age classes of foliage samples were harvested and the phenolic compounds extracted, separated by high performance liquid chromatography and identified and quantified by diode-array spectrometry and mass spectrometry. Foliar phenolic concentration was greater in 1x- and 2x-treated tissue than in 0x-treated tissue. Phenolic compounds that increased in response to UV-B radiation were predominantly flavonoids, primarily quercetin and kaempferol glycosides. Enhancement of UV-B radiation from 1x to 2x ambient concentration did not result in further flavonoid accumulation in either greenhouse or field ramets; however, a non-flavonoid phenolic glycoside, salicortin, increased in response to an increase in UV-B radiation from 1x to 2x ambient concentration. Increased salicortin concentrations accounted for at least 30-40% of the total (5%) increase in UV-absorption potential of 2x-treated tissue. Because salicortin and other salicylates are important in plant-herbivore-predator relationships, these increases are discussed in the context of collateral feeding studies. We conclude that enhanced solar UV-B radiation may significantly alter trophic structure in some ecosystems by stimulating specific phenolic compounds.

Quantitative determination of geosmin in red beets (Beta vulgaris L.) using headspace solid-phase microextraction

An improved analytical method for the determination of geosmin in red beets was developed using headspace solid-phase microextraction (HSPME). Volatiles of beet juice were extracted in headspace for 2 h using a polydimethylsiloxane/divinylbenzene fiber, thermally desorbed from the fiber, and analyzed by gas chromatography. The HSPME method was determined to be suitable for geosmin analysis as evidenced by high relative recovery (99.2%), low relative standard deviation (7.48%), and reasonable detection limit (1 microg/kg of beet root tissue). The concentrations of geosmin in four beet cultivars ranged from 9.69 +/- 0.22 to 26.7 +/- 0.27 microg/kg, depending on cultivar.

Biosynthetic origin of geosmin in red beets (Beta vulgaris L.)

Geosmin provides the characteristic but sometimes undesirable "earthy" flavor to red table beets. To date, it is not known whether geosmin is a byproduct of beet metabolism or synthesized by soil-borne microorganisms and taken up by the beets during maturation. Analysis of mature beet roots revealed that peels contained 6 times the amount of geosmin compared to the bodies and cores. Sterilized beet seeds were aseptically grown in a basal medium prior to analysis for the presence of geosmin. Using a headspace solid-phase microextraction (HSPME) method, the relative recovery of geosmin from beet seedling extracts was 72.0 +/- 4.2% with (-)-menthone as the internal standard. The presence of geosmin in aseptically grown beet seedlings was confirmed by gas chromatography-mass spectrometry using authentic geosmin as the standard. During aseptic growth, the concentration of geosmin in seedlings remained constant for up to 5 months but increased at 6 months. Geosmin added to the growth medium was not absorbed by the seedlings. These studies support the conclusion that red beets are capable of endogenous synthesis of geosmin.

Investigations of aroma volatile biosynthesis under anoxic conditions and in different tissues of "Redchief Delicious" apple fruit (Malus domestica Borkh.)

Disks from different tissues were obtained from "Redchief Delicious" apple fruit (Malus domestica Borkh.) and analyzed for the ability to metabolize 1-pentanol as well as synthesize constitutive esters and alcohols under anoxic and aerobic conditions. The skin tissue displayed a greater capacity to synthesize pentanal, pentyl acetate, pentyl propionate, pentyl butyrate, and pentyl hexanoate than the hypanthial and carpellary tissues during incubation with 1-pentanol. With the exception of pentyl acetate and pentyl propionate biosynthesis, the hypanthial tissue synthesized these compounds at a higher rate than the carpellary tissue. Anoxia inhibited both constituent and 1-pentanol-derived ester biosynthesis. While anoxia inhibited ester biosynthesis, ethanol biosynthesis increased at a greater rate in tissue disks held under these conditions. Biosynthesis of 1-butanol, 2-methyl-1-butanol, and 1-hexanol was greater in tissue disks held in air during the first part of the measurement period and dropped off more rapidly than those transpiring in tissue disks held under anoxic conditions. The biosynthetic rates of all esters, both constituent and 1-pentanol-derived, increased as a result of air exposure. While hypoxic or anoxic conditions may promote ethanol synthesis, these conditions also appear to inhibit the formation of the ethanol-derived esters partially responsible for the off-flavor in apples attributed to ultralow O(2) controlled atmosphere storage.

Alteration of foliar flavonoid chemistry induced by enhanced UV-B radiation in field-grown Pinus ponderosa, Quercus rubra and Pseudotsuga menziesii

Chromatographic analyses of foliage from several tree species illustrate the species-specific effects of UV-B radiation on both quantity and composition of foliar flavonoids. Pinus ponderosa, Quercus rubra and Pseudotsuga menziesii were field-grown under modulated ambient (1x) and enhanced (2x) biologically effective UV-B radiation. Foliage was harvested seasonally over a 3-year period, extracted, purified and the flavonoid fraction applied to a mu Bondapak/C(18) column HPLC system sampling at 254 nm. Total flavonoid concentrations in Quercus rubra foliage were more than twice (leaf area basis) that of the other species; Pseudotsuga menziesii foliage had intermediate levels and P. ponderosa had the lowest concentrations of total flavonoids. No statistically significant UV-B radiation-induced effects were found in total foliar flavonoid concentrations for any species; however, concentrations of specific compounds within each species exhibited significant treatment effects. Higher (but statistically insignificant) levels of flavonoids were induced by UV-B irradiation in 1- and 2-year-old P. ponderosa foliage. Total flavonoid concentrations in 2-year-old needles increased by 50% (1x ambient UV-B radiation) or 70% (2x ambient UV-B radiation) from that of 1-year-old tissue. Foliar flavonoids of Q. rubra under enhanced UV-B radiation tended to shift from early-eluting compounds to less polar flavonoids eluting later. There were no clear patterns of UV-B radiation effects on 1-year-old P. menziesii foliage. However, 2-year-old tissue had slightly higher foliar flavonoids under the 2x UV-B radiation treatment compared to ambient levels. Results suggest that enhanced UV-B radiation will alter foliar flavonoid composition and concentrations in forest tree species, which could impact tissue protection, and ultimately, competition, herbivory or litter decomposition.

Formation of volatile branched chain esters in bananas (Musa sapientum L.)

Substrates controlling the formation of branched chain volatile esters in ripening bananas were investigated by the application of alcohol and amino acid precursors to whole fruit and tissue samples. The resulting changes in the profile of the volatile esters were determined using SPME and GC. These changes revealed the selectivity characteristics of the esterification enzyme AAT, the availability of acyl CoA's for ester formation, and the role of substrate supply on volatile production. The results obtained suggest that substrate supply is a major determinant of the quantitative and qualitative composition of the resulting aroma profile.

Biosynthesis of Sucrose and Mannitol as a Function of Leaf Age in Celery (Apium graveolens L.)

In celery (Apium graveolens L.), the two major translocated carbohydrates are sucrose and the acyclic polyol mannitol. Their metabolism, however, is different and their specific functions are uncertain. To compare their roles in carbon partitioning and sink-source transitions, developmental changes in (14)CO(2) labeling, pool sizes, and key enzyme activities in leaf tissues were examined. The proportion of label in mannitol increased dramatically with leaf maturation whereas that in sucrose remained fairly constant. Mannitol content, however, was high in all leaves and sucrose content increased as leaves developed. Activities of mannose-6-P reductase, cytoplasmic and chloroplastic fructose-1,6-bisphosphatases, sucrose phosphate synthase, and sucrose synthase increased with leaf maturation and decreased as leaves senesced. Ribulose bisphosphate carboxylase and nonreversible glyceraldehyde-3-P dehydrogenase activities rose as leaves developed but did not decrease. Thus, sucrose is produced in all photosynthetically active leaves whereas mannitol is synthesized primarily in mature leaves and stored in all leaves. Onset of sucrose export in celery may result from sucrose accumulation in expanding leaves, but mannitol export is clearly unrelated to mannitol concentration. Mannitol export, however, appears to coincide with increased mannitol biosynthesis. Although mannitol and sucrose arise from a common precursor in celery, subsequent metabolism and transport must be regulated separately.