J.M. Monaghan

The use of grain protein deviation for identifying wheat cultivars with high grain protein concentration and yield

The relationship between grain protein concentration and grain yield in different cultivars of winter wheat was examined in a series of field experiments carried out over three years, in which 13, 12 and 8 cultivars were studied in each year, respectively. The plants were grown at sites located in Shropshire, west-central England, in years 1 and 2, and at three other locations in eastern England in year 3. Above ground plant samples were collected at an thesis and again at maturity, when they were separated into grain and straw, and analysed for dry matter and N content. Analysis of residuals from regression of grain protein concentration on grain yield (grain protein deviation, GPD) showed that some cultivars had a higher grain protein concentration than was predicted from grain yield alone. It was deduced that the capacity to accumulate a higher grain protein concentration than predicted from grain yield is under genetic control and thus may be improved through breeding. Other factors (weight of N accumulated in the biomass at anthesis, weight of N accumulated in the biomass between anthesis and maturity and the concentration of N remaining in the straw at maturity) were added step-wise into the regression to enable statistical analysis of their relative contributions to grain protein. High GPD may be achieved through increased N accumulation after anthesis, combined with efficient re-translocation of vegetative N reserves. The use of GPD provides a selection criteria in wheat breeding programs to screen for increased grain protein concentration without a concurrent grain yield reduction.

The air-borne distribution of zoonotic agents from livestock waste spreading and microbiological risk to fresh produce from contaminated irrigation sources

Aims:  To assess the risks of zoonotic agents in dissemination of livestock wastes into the environment by airborne distribution. To subsequently assess the survival time of zoonotic agents, introduced in irrigation water, on the phylloplane of produce.

Irrigation water quality for leafy crops: A perspective of risks and potential solutions

There is increasing evidence of the contribution of irrigation water in the contamination of produce leading to subsequent outbreaks of foodborne illness. This is a particular risk in the production of leafy vegetables that will be eaten raw without cooking. Retailers selling leafy vegetables are increasingly targeting zero-risk production systems and the associated requirements for irrigation water quality have become more stringent in regulations and quality assurance schemes (QAS) followed by growers. Growers can identify water sources that are contaminated with potential pathogens through a monitoring regime and only use water free of pathogens, but the low prevalence of pathogens makes the use of faecal indicators, particularly E. coli, a more practical approach. Where growers have to utilise water sources of moderate quality, they can reduce the risk of contamination of the edible portion of the crop (i.e., the leaves) by treating irrigation water before use through physical or chemical disinfection systems, or avoid contact between the leaves and irrigation water through the use of drip or furrow irrigation, or the use of hydroponic growing systems. This study gives an overview of the main problems in the production of leafy vegetables associated with irrigation water, including microbial risk and difficulties in water monitoring, compliance with evolving regulations and quality standards, and summarises the current alternatives available for growers to reduce microbial risks.

Sulphur nutrition: An important factor for the quality of wheat and rapeseed

The incidence of sulphur (S) deficiency has increased in many crops in the U.K. and other European countries in the last 10 years. Apart from the effects on yield, the S nutrition of a crop often has a strong influence on the quality of the produce. We have shown that S fertilisation significantly improved breadmaking quality of field-grown wheat (Triticum aestivum L.) in the U.K. with the loaf volumes of the same variety grown at different sites correlating better with the concentrations of grain S than grain N. Sulphur also increased gel protein content of flour, but decreased its elastic strength. In contrast, application of S fertilisers to oilseed rape (Brassica napus L.) can lead to increased glucosinolate concentrations in the seed which exceed the limit for the meal to be used in animal feeds. Results from 29 field experiments showed that the glucosinolate concentration of rapeseed was usually higher when grown at the S-sufficient than the S-deficient sites. However, the addition of S fertiliser increased the glucosinolate concentration much more under S-deficient than under S-sufficient conditions. Furthermore, there was a strong interaction between N and S on seed glucosinolates. Increasing N decreased the glucosinolate concentration when S was deficient, but increased the glucosinolate concentration when S was applied. The need to maintain a balanced N and S supply for both yield and quality is stressed.

Distribution and decline of human pathogenic bacteria in soil after application in irrigation water and the potential for soil‐splash‐mediated dispersal onto fresh produce

Aims:  To improve our understanding of the survival and splash‐mediated transfer of zoonotic agents and faecal indicator bacteria introduced into soils used for crop cultivation via contaminated irrigation waters.

Responses of breadmaking quality to sulphur in three wheat varieties

Field experiments were carried out at three sites in England to investigate the effects of S fertilisation on breadmaking quality of three winter wheat varieties (Hereward, Rialto and Spark) in the 1996-1997 season. The soils at the three sites differed in extractable S contents. Depending on site, either 180 and 230 kg ha(-1) N or 230 and 280 kg ha(-1) N treatments were factorially combined with three S treatments (0, 20 and 100 kg ha(-1) S). Addition of S increased loaf volume significantly at two sites where grain S concentration was also significantly increased and grain N:S ratio decreased. Application of the extra 50 kg ha(-1) N increased grain protein concentration but did not increase loaf volume at any of the sites. Loaf volume was found to correlate more closely with grain S than with grain protein concentration. Addition of S generally decreased the elastic modulus of gel protein and dough resistance but increased dough extensibility. Despite considerable differences in their dough rheology, the responses in rheology and loaf volume to S were similar in all three varieties. Selected flour samples of Rialto from the Bridgets site were also analysed for the glutenin subunit distribution, showing that S addition increased the relative proportion of low-molecular-weight subunits at the expense of high-molecular-weight subunits of glutenin. This study therefore shows that the beneficial effects of S on breadmaking quality are associated with decreased dough elasticity and increased extensibility resulting from effects on the amount and composition of the glutenin polymers. The results also indicate that S fertilisation is required in some areas of England to maintain breadmaking quality

High- but not low-intensity light leads to oxidative stress and quality loss of cold-stored baby leaf spinach

BACKGROUND Quality management in the fresh produce industry is an important issue. Spinach is exposed to various adverse conditions (temperature, light, etc.) within the supply chain. The present experiments were conducted to investigate the effect of light conditions (dark, low-intensity light (LL) and high-intensity light (HL)) and photoperiod (6 h HL and 18 h dark) on the quality changes of cold-stored spinach. RESULTS HL exposure resulted in oxidative stress, causing tissue damage and quality loss as evidenced by increased membrane damage and water loss. The content of total ascorbic acid was reduced under HL conditions. On the other hand, storage of spinach under LL conditions gave promising results, as nutritional quality was not reduced, while texture maintenance was improved. No significant differences, with the exception of nutritional quality, were found between spinach leaves stored under continuous (24 h) low-intensity light (30-35 µmol m(-2) s(-1)) and their counterparts stored under the same light integral over 6 h (130-140 µmol m(-2) s(-1)). CONCLUSION LL extended the shelf-life of spinach. The amount of light received by the leaves was the key factor affecting produce quality. Light intensity, however, has to be low enough not to cause excess oxidative stress and lead to accelerated senescence.

Quantifying the impact of exogenous abscisic acid and gibberellins on pre-maturity α-amylase formation in developing wheat grains

To study the role of abscisic acid (ABA) and gibberellins (GA) in pre-maturity α-amylase (PMA) formation in developing wheat grain, two glasshouse experiments were conducted under controlled conditions in the highly PMA-susceptible genotype Rialto. The first, determined the relative efficacy of applying hormone solutions by injection into the peduncle compared to direct application to the intact grain. The second, examined the effects of each hormone, applied by either method, at mid-grain development on PMA in mature grains. In the first experiment, tritiated ABA (3H-ABA) and gibberellic acid (3H-GA3) were diluted with unlabelled ABA (100 µM) and GA3 (50 µM), respectively, and applied at mid-grain development using both methods. Spikes were harvested after 24, 48 and 72 h from application, and hormone taken up by grains was determined. After 72 h, the uptake per grain in terms of hormones applied was approximately 13% for ABA and 8% for GA3 when applied onto the grains, and approximately 17% for ABA and 5% for GA3 when applied by injection. In the second experiment, applied ABA reduced, whereas applied GA3 increased α-amylase activity. This confirmed that exogenously applied ABA and GA were absorbed in sufficient amounts to alter grain metabolism and impact on PMA.

Deficit irrigation reduces postharvest rib pinking in wholehead Iceberg lettuce, but at the expense of head fresh weight

BACKGROUND Postharvest pinking is a serious issue affecting lettuce quality. Previous studies suggested the possibility of using deficit irrigation to control discolouration; however, this approach may also affect yield. This study investigated the effect of varying irrigation deficits on iceberg lettuce (Lactuca sativa L.) to determine the relationship between irrigation deficit, pinking and fresh weight. RESULTS The deficit imposed and head fresh weight obtained depended on both the duration and timing of withholding irrigation. Withholding irrigation for a period of 2 or 3 weeks in the middle or end of the growth period significantly reduced rib pinking compared to well-watered controls. Withholding irrigation for 2 weeks at the start of the growth period or 1 week at the end did not significantly reduce pinking. Withholding irrigation also reduced head fresh weight such that minimising pinking would be predicted to incur a loss of 40% relative to well-watered controls. However, smaller benefits to pinking reduction were achieved with less effect on head fresh weight. CONCLUSION Deficit irrigation could be used to provide smaller but higher quality heads which are less likely to be rejected. The balance of these factors will determine the degree of adoption of this approach to growers.

Risk Assessment or Assessment of Risk? Developing an Evidence-Based Approach for Primary Producers of Leafy Vegetables To Assess and Manage Microbial Risks

Over the last 10 years, some high-profile foodborne illness outbreaks have been linked to the consumption of leafy greens. Growers are required to complete microbiological risk assessments (RAs) for the production of leafy crops supplied either to retail or for further processing. These RAs are based primarily on qualitative judgements of hazard and risks at various stages in the production process but lack many of the steps defined for quantitative microbiological RAs by the Codex Alimentarius Commission. This article is based on the discussions of an industry expert group and proposes a grower RA approach based on a structured qualitative assessment, which requires all decisions to be based on evidence and a framework for describing the decision process that can be challenged and defended within the supply chain. In addition, this article highlights the need for evidence to be more easily available and accessible to primary producers and identifies the need to develop hygiene criteria to aid validation of proposed interventions.