Modesto Olanya

Effect of native microflora, waiting period, and storage temperature on Listeria monocytogenes serovars transferred from cantaloupe rind to fresh-cut pieces during preparation.

The most recent outbreak of listeriosis linked to consumption of fresh-cut cantaloupes indicates the need to investigate the behavior of Listeria monocytogenes in the presence of native microflora of cantaloupe pieces during storage. Whole cantaloupes were inoculated with L. monocytogenes (10(8)-CFU/ml suspension) for 10 min and air dried in a biosafety cabinet for 1 h and then treated (unwashed, water washed, and 2.5% hydrogen peroxide washed). Fresh-cut pieces (∼3 cm) prepared from these melons were left at 5 and 10°C for 72 h and room temperature (20°C) for 48 h. Some fresh-cut pieces were left at 20°C for 2 and 4 h and then refrigerated at 5°C. Microbial populations of fresh-cut pieces were determined by the plate count method or enrichment method immediately after preparation. Aerobic mesophilic bacteria, yeast and mold of whole melon, and inoculated populations of L. monocytogenes on cantaloupe rind surfaces averaged 6.4, 3.3, and 4.6 log CFU/cm(2), respectively. Only H(2)O(2) (2.5%) treatment reduced the aerobic mesophilic bacteria, yeast and mold, and L. monocytogenes populations to 3.8, 0.9, and 1.8 log CFU/cm(2), respectively. The populations of L. monocytogenes transferred from melon rinds to fresh-cut pieces were below detection but were present by enrichment. Increased storage temperatures enhanced the lag phases and growth of L. monocytogenes. The results of this study confirmed the need to store fresh-cut cantaloupes at 5°C immediately after preparation to enhance the microbial safety of the fruit.

Effect of Hydrogen Peroxide in Combination with Minimal Thermal Treatment for Reducing Bacterial Populations on Cantaloupe Rind Surfaces and Transfer to Fresh-Cut Pieces

Surface structure and biochemical characteristics of bacteria and produce play a major role in how and where bacteria attach, complicating decontamination treatments. Whole cantaloupe rind surfaces were inoculated with Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes at 10(7) CFU/ml. Average population size of Salmonella, Escherichia coli O157:H7, and L. monocytogenes recovered after surface inoculation was 4.8 ± 0.12, 5.1 ± 0.14, and 3.6 ± 0.13 log CFU/cm(2), respectively. Inoculated melons were stored at 5 and 22°C for 7 days before washing treatment interventions. Intervention treatments used were (i) water (H2O) at 22°C, (ii) H2O at 80°C, (iii) 3% hydrogen peroxide (H2O2) at 22°C, and (iv) a combination of 3% H2O2 and H2O at 80°C for 300 s. The strength of pathogen attachment (SR value) at days 0, 3, and 7 of storage was determined, and then the efficacy of the intervention treatments to detach, kill, and reduce transfer of bacteria to fresh-cut pieces during fresh-cut preparation was investigated. Populations of E. coli O157:H7 attached to the rind surface at significantly higher levels (P < 0.05) than Salmonella and L. monocytogenes, but Salmonella exhibited the strongest attachment (SR value) at all days tested. Washing with 3% H2O2 alone led to significant reduction (P < 0.05) of bacteria and caused some changes in bacterial cell morphology. A combination treatment with H2O and 3% H2O2 at 8°C led to an average 4-log reduction of bacterial pathogens, and no bacterial pathogens were detected in fresh-cut pieces prepared from this combination treatment, including enriched fresh-cut samples. The results of this study indicate that the microbial safety of fresh-cut pieces from treated cantaloupes was improved at day 6 of storage at 5°C and day 3 of storage at 10°C.

Comparative assessment of pest management practices in potato production at Farmer Field Schools

Farmer field schools (FFS) and other participatory approaches are useful methods for rapid delivery of agricultural technologies, knowledge, and information in resource-constrained agro-ecosystems. Cultivar selection, weekly fungicide applications and integrated disease management (IDM) based on a disease monitoring strategy were evaluated at FFS for late blight control. Farmers’ knowledge and perceptions of pest management and agronomic practices were also assessed for both FFS participants and non-participants from 1999–2002. Late blight development and tuber yield varied among field schools, but cultivars had significant effects on late blight severity and yield over a range of disease management options relative to the untreated check. FFS participants and non-participants used diverse sources of pest management information, but differed significantly (P < 0.05) in their use of management methods and practices. Cultivar resistance and fungicides were ranked as major components of pest control by 18%–85% and 7%–30% of FFS participants and non-participants, respectively. Differences in knowledge of cropping practices and pest biology, causal agents, disease symptoms, factors favoring disease development and cultural management of insects and storage pests were recorded. Participatory field experiments, access to resistant cultivars, disease management and use of various agronomic practices learnt at FFS can greatly improve pest control and potato production.

Injury and Viability Loss of Escherichia coli O157:H7, Salmonella, Listeria Monocytogenes and Aerobic Mesophilic Bacteria in Apple Juice and Cider Amended with Nisin-Edta

For health reasons, people are consuming fresh juices or minimally processed fruit and vegetable juices, thereby, exposing themselves to the risk of foodborne illness if such juices are contaminated with bacteria pathogens. Behavior of aerobic mesophilic bacteria, Escherichia coli O157:H7, L. monocytogenes and Salmonella cells at 104 CFU/ml in apple cider (pH 3.9) and apple juice (pH 3.6), amended with nisin (500 IU/ml)+ethylene diaminetetraacetic acid (EDTA, 0.02 M) combination treatment and storage at 5°C and 10°C for 10 days as well as 22oC for 16 h was investigated. Populations of aerobic mesophilic bacteria increased in untreated apple cider stored at 5°C and 10°C for 10 days while E. coli O157:H7, L. monocytogenes and Salmonella slightly declined. A slight increase for E. coli O157:H7, L. monocytogenes and Salmonella in juices stored at room temperature (22°C) was observed. Treatment of juices with nisin+EDTA led to higher inactivation of bacterial populations including inoculated populations of E. coli O157:H7, L. monocytogenes and Salmonella. The surviving populations determined within 10 to 30 min of treatment include 18% of injured cells. And leakage of UV- absorbing materials were higher in samples containing the injured bacteria. The injured populations did not recover during storage at 5 or 22°C. Waiting up to 4 h before refrigeration of treated samples and leaving treated refrigerated samples at room temperature for up to 4 h did not cause significant changes in microbial populations. Addition of nisin+EDTA combination in unpasteurized apple cider or apple juice as a natural antimicrobial will improve the microbial safety of the juices. However, treatment of juices with nisin+EDTA combination is still subject to regulatory approval by the FDA.

Efficacy of fungicide combinations, phosphoric acid and plant extract from stinging nettle on potato late blight management and tuber yield

Late blight caused by Phytophthora infestans is a major constraint to potato production. Inadequate control of the disease has often resulted in potato yield losses. We assessed the efficacy of fungicides, phosphoric acid and stinging nettle extract combinations for late blight control at two locations in Kenya. Disease severity, relative area under disease progress curves (RAUDPC), pathogen lesions and tuber yield were quantified during the 2008 and 2009 cropping cycles. The application of metalaxyl alternated with phosphate resulted in the greatest suppressive effects on late blight. The average late blight severity ranged from 3.5 to 34% in 2008 and 4.7 to 50% in 2009 at Tigoni location. RAUDPC for the same location ranged from 5 to 40% and 5 to 50% in 2008 and 2009, respectively. Similar levels of late blight severity were recorded at Marimba location in both years. Lesion growth and pathogen lesion numbers on potato plants differed significantly (p < 0.05) among treatments. Fungicides, phosphoric acid and stinging nettle extract varied in late blight control. Potato tuber yield varied among treatments. Phosphoric acid treatment had significantly (p < 0.05) greater tuber yield compared to metalaxyl at both locations. Field plots treated with plant extracts from stinging nettle resulted in the lowest tuber yield compared to other treatments with the exception of the untreated control. Fungicides, phosphoric acid, stinging nettle extract and their combinations can be readily effective in the suppression of late blight severity and pathogen lesions with moderate increases in tuber yield.

Principles of Food Preservation

Food preservation is an action or method used to maintain foods at certain desirable properties or quality to obtain maximum benefit. A good method of food preservation is one that slows down or prevents altogether the action of the agents of spoilage without damaging the food. To achieve this, certain basic methods are applied depending on the food types. Food preservation has been an essential activity throughout human history. The cycle of seasons brings periods of shortage and abundance of various foods at different times of the year. Preservation makes it possible to consume some of these foods during off seasons, throughout the year. Food preservation usually involves controlling or preventing growth of microrganisms or minimizing the quality degradation due to microbial spoilage or unwanted chemical changes in foods such as rancidity due to oxidation of fats over time. Preservation of foods is no longer simple and straightforward today; it has evolved to a highly inter-disciplinary field of science. In recent years, many new sophisticated preservation techniques have developed to extend the quality and shelf-life, minimize risk, protect the environment, and improve functional, sensory, and nutritional properties. Many of emerging preservation technologies have already reached commercial adoption in specific applications while many others remain promising. Development of suitable equipment, especially for continuous processing for a variety of foods and standardization of the process parameters for easy regulatory approval will pave the way for improved food preservation. The objective of this chapter was to examine the science and technology involved in the manipulation of conventional as well as sophisticated emerging preservation methods.

Intervention technologies for food safety on minimally processed produce: Perspectives on foodborne and plant pathogens

T study aims to compare the quality characteristics of steamed rice cake added with diluent water at different ratios and applying steam for various times. Rice cake was prepared with two levels of water (60, 65%) and by steaming for 6, 8 and 10 min. The central temperature of rice cake in steamer was measured for 10 min. The maximum temperature of rice cake with 65% water content was 101.0±0.20C with the steepest gradient in increasing temperature slope among rice cakes prepared with two levels of water content. It indicated that there is a relationship between water content and steaming temperature profile. Texture analysis profile of steamed rice cakes were investigated by compression test. The rice cake with 60% water content and which was steamed for 6 min (W65_S6) showed the highest value in hardness (46.93±2.04 N) and adhesiveness (29.18±4.14 N. Sec). In conclusion, these results can be helpful to optimize steam processing and adding water content to achieve desirable quality, texture, and mouth feel of steamed rice cake.S is fished mainly in Japan and Taiwan, and is often preserved using salt. Salt has the effects of maintaining a taste component and suppressing bacterial growth. The taste component of the fish is inosinic acid (IMP), which is degraded to non-taste components by IMP-degrading enzyme (IMPase). The ratio of dark muscle in all saury muscle is approximately 40%. Previous studies have reported that the properties of IMPase in white muscle are different from the properties of IMPase in dark muscle. In this study, we investigated the effect of various salts (NaCl, MgCl2, CaCl2, MgSO4, and Na2SO4) on IMPase activity in the white and dark muscle of saury. Enzyme extracted from white or dark muscle was added to reaction mixtures containing IMP and various final concentrations of salt (0.33–1.67%), and we measured the IMPase activity. In white muscle, the activity was suppressed by all the salts examined at a final concentration of more than approximately 0.5%. However, although IMPase activity in dark muscle was suppressed by NaCl, Na2SO4, and CaCl2 at final concentrations of more than approximately 0.4%, the activity was accelerated by MgCl2 at a final concentration of less than 1.5% and MgSO4 at a final concentration of 0.33-1.67 %. It was thus found that different salts have different effects on IMPase in the white and dark muscle of saury.W is one of the main residues from the dairy industry, particularly from the cheese production. It contains water, lactose, salts and soluble proteins. Enzymatic hydrolysis has been used in order to improve some of the activities attributed to the whey proteins, since it results in peptides with different amino acid sequences and molecular sizes. The aim of this study was to evaluate the influence of substrate pretreatment on the kinetics of enzymatic hydrolysis of whey proteins using the enzymes Alcalase and Flavourzyme. The evaluated substrates were: fresh acid whey, reconstituted powdered whey protein concentrate and whey protein concentrated by ultrafiltration. The effect of an endopeptidase and an exopeptidase on the kinetics of enzymatic hydrolysis was evaluated. Results were fitted by an empirical model, which is function of degree of hydrolysis (DH) and processing time. The highest DH (%) was obtained using the endopeptidase Alcalase to hydrolyse the fresh whey, reaching 63%, which was due to a possible unfolding of the protein molecule, caused by prior freezing to which this substrate was subjected. The ultrafiltered and reconstituted samples presented DH values of 57 and 27%, respectively. For Flavourzyme, all the substrates presented lower values of DH than those hydrolysed by Alcalase (10 20%). The kinetic equation proved to be adequate for modeling enzymatic reaction for milk whey proteins, showing a good fit to the experimental data (R2 > 0.986).I this study infant formula was subject to different heat treatment preparations; boiling, microwaving and powder with boiled water. Each treatment was analyzed using a charged aerosol detector for the simultaneous determination of eicosapentaenoic acid (EPA) 20:5(n-3), decosahexaenoic acid (DHA) 22:6 (n-3), arachidonic acid (AA) 20:4 (n-6), linoleic acid (LA) 18:2 (n-6) and alpha linolenic acid (ALA) 18:3 (n-3) to look for changes in these fatty acids. There were statistical changes in LA and ALA between certain treatments. In conclusion the heat treatments of the infant formulas are subjected to do within the instruction advised on the label of the products, does not appear to majorly effect the concentration of the investigated fatty acids, however there is a wide variation of the fatty acids investigated between different brands on the UK market.

Effects of Early and Late Harvest on Agronomic Performance and Stability of Late Blight Resistant (R-gene Free) Potato Genotypes

Late blight is an important constraint to potato production and genotype resistance is an effective disease control mesure. Ten late blight resistant potato genotypes (R-gene free) were assessed for yield performance and stability at early (90 days) and late harvest (120 days) at two locations in Kenya during two years. Significant differences (P ≤ 0.05) in area under disease progress curves (AUDPC) were detected among potato genotypes. Resistant genotypes free of R-genes had significantly (P ≤ 0.05) higher yield at late than early harvest, perhaps due to increased tuber bulking period. The rank of genotypes for AUDPC, late blight resistance, and tuber yield varied across seasons and locations (environment). Additive main effects and multiplicative interaction (AMMI) analysis of tuber yield and late blight resistance resulted in significant (P ≤ 0.05) effects of genotypes (G) and environments (E). The proportion of genotypic variance was larger than the environmental variance and the G × E interactions. For tuber yield, the G, E, and G × E interactions accounted for 42.9, 39.6 and 17.5%; and 53.4, 29.7, and 16.9% at early and late harvests, respectively. For AUDPC, G, E, and G × E accounted for 80.2, 5.0, and 14.8%; as well as 82.3, 4.6, and 13% for early and late harvests, respectively. The resistance of potato genotypes without R-genes varied. Selective deployment of resistant genotypes can improve potato tuber yield.

Optimization of Late Blight and Bacterial Wilt Management in Potato Production Systems in the Highland Tropics of Africa

Late blight and bacterial wilt are two formidable disease constraints on potato and account for significant losses in Sub-Saharan Africa (SSA). In this chapter, various management techniques for late blight and bacterial wilt diseases are highlighted with examples drawn from diverse research. The modified disease management approaches include resistant cultivars, reduced fungicide applications, disease monitoring based on field scouting, cultural practices, post-harvest management and farmer training. Deployment of cultivars with resistance genes and quantitative resistance in addition to fungicide use has contributed significantly to sustained late blight management in tropical Africa. Similarly, cultural practices such as date of planting, disease-free tubers, roguing and bio-rational approaches (plant-derived extracts and phosphoric acid) have been used to a lesser degree. Disease monitoring and weather-based predictions in relation to fungicide applications have been utilized in conjunction with host-plant resistance. Similarly, bacterial wilt has been successfully managed through non-chemical means which include crop rotation, sanitation (removal of wilted plants, destruction of crop residues), and minimum post-emergence cultivation of potatoes. Small-scale seed plot technique, non-diseased tubers, soil amendments and less susceptible cultivars have been important components for integrated management of bacterial wilt disease. The holistic approach for control of late blight and bacterial wilt ultimately lead to increased potato production and better economic returns in the diverse potato production region of SSA.