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Call number: LD2668 .T4 1978 B65 / Master of Science

Call number: LD2668 .T4 1978 L55 / Master of Science

Call number: LD2668 .T4 1984 R515 / Master of Science

Thesis (MSc Food Sc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Kefir is a fermented dairy beverage resulting from the fermentation of milk with reusable Kefir grains. The grains consist of a complex combination of lactic acid bacteria and yeasts in a symbiotic relationship, embedded in a polysaccharide matrix called kefiran. Various problems are experienced during the commercialisation of the ready-made Kefir beverage and, therefore, it is more advantageous to market the grains, enabling the consumer to produce the beverage at home. Kefir grains could be mass-cultured and then preserved by Iyohilisation for successful long-term storage and easy distribution, during commercialisation. The microbial balance of the Kefir grains changes during both mass-culturing and freeze-drying, which will have an influence on the sensory properties of the Kefir beverage produced. The aim of this study was the optimisation of the production of Kefir from mass-cultured grains and from freezedried mass-cultured grains respectively. The sensory characteristics of the fermented beverages produced from these mass-cultured and preserved grains were determined. Mass-cultured Kefir grains were activated and Kefir produced using nine methods with different activation times and temperatures, different grain:milk ratios (36, 72 and 108 g grains.l⁻¹) and with different heat-treated milks (pasteurised, double pasteerised and UHT). The best Kefir beverage was produced by activation of the grains at 22°C for two successive 24 h incubation periods, followed by Kefir production at 22°C for 18 h and a maturation period at 18°C for 6 h. The milk was replaced before every incubation period, excluding the maturation period, and the fermentation vessel was swirled five times at the start of fermentation and after 18 h. This method resulted in a sour beverage with a thick consistency and the characteristic effervescence and flavour of Kefir. The optimal grain:milk ratio was identified as 36 g grains.l⁻¹ and the best heat-treated milks for the production of Kefir beverage were UHT and double pasteurised milk. Mass-cultured Kefir grains were freeze-dried for 1, 2, 3 and 6 d and the moisture loss determined. Freeze-dried grains were rehydrated for 1, 2, 6, 12 and 18 h to determine the optimal rehydration time. A sensory analysis was performed to compare the properties of Kefir produced from mass-cultured grains (Me), freeze-dried mass-cultured grains that were rehydrated and activated (FDRA) and activated mass-cultured grains that were freeze-dried and rehydrated (AFDR). The chemical compositions of mass-cultured grains (MC), mass-cultured, freezedried grains (MCFD), mass-cultured, freeze-dried grains that were rehydrated and activated (FDRA) and activated mass-cultured grains that were freeze-dried and rehydrated (AFDR), were also investigated. The optimum time to freeze-dry grains was 2 d and to rehydrate freeze-dried gtains was 1 h. The sensory analysis indicated that Kefir beverages prepared from FDRA and AFDR grains did not differ significantly and were less fermented than Kefir produced from MC grains. It was concluded that Kefir with excellent sensory characteristics can be produced from mass-cultured grains. Freeze-drying is a better method to preserve Kefir grains than freezing due to mass loss during freezing and easier distribution and storage of freeze-dried grains. The supplementation of freeze-dried grains with additional lactic acid bacteria and yeast isolates should be investigated. / AFRIKAANSE OPSOMMING: Kefir is 'n gefermenteerde suiwelproduk wat geproduseer word deur die fermentasie van melk met herbruikbare Kefirkorrels. Die korrels bestaan uit 'n komplekse kombinasie van melksuurbakterië en giste en is ingebed in 'n polisakkaried matriks genaamd kefiran. Verskeie probleme word ondervind met die kommersialisering van die klaar voorbereide Kefirdrankie en dit is meer voordelig om die korrels te bemark. Dit sal die verbruiker daartoe in staat stel om self Kefir tuis te produseer. Kefirkorrels kan in massa gekweek word en dan gevriesdroog word om langtermyn storing en verspreiding te vergemaklik tydens kommersialisering. Die spesifieke mikrobiese balans van die Kefirkorrels word tydens massakweking en vriesdroging versteur. Dus sal hierdie twee prosesse 'n invloed hê op die sensoriese eienskappe van die Kefir drankie geproduseer. Die doel van hierdie studie was die optimisering van die produksie van Kefir vanaf massagekweekte korrels en gevriesdroogde massagekweekte korrels. Die sensoriese karakteristieke van die Kefir geproduseer met hierdie korrels is ondersoek. Massagekweekte Kefirkorrels is geaktifeer en Kefir is geproduseer met nege verskillende metodes met variasies in die tyd en temperatuur kombinasies, verskillende korrel:melk verhoudings (36, 72 en 108g korrels.l⁻¹) en verskillende hittebehandelde melke (gepasteuriseerd, dubbel gepasteuriseer en UHT). Die beste Kefirdrankie is geproduseer deur die aktivering van die korrels by 22°C vir twee 24 h inkubasieperiodes, gevolg deur Kefir produksie by 22°C vir 18 uur en 'n verouderingsperiode by 18°C vir 6 h. Die melk was voor elke inkubasieperiode vervang, uitsluitende die verouderingsperiode. Die fermentasie houer is vyf maal gedraai aan die begin van fermentasie en na 12 h. Hierdie metode het gelei tot 'n drankie wat suur was met 'n dik konsistensie en die karakteristieke vonkeling en geur van Kefir. Die optimale korrel:melk ratio is geidentifiseer as 36 9 korrels.l⁻¹ en die verkieslike hittebehandelde melke is dubbel gepasteuriseerde en UHT melk. Massagekweekte Kefirkorrels was vir 1, 2, 3 en 6 dae gévriesdroog en die massaverlies is bepaal. Gevriesdroog korrels is gerehidreer vir 1, 2, 6, 12 en 18 h om die optimale rehidrasietyd te bepaal. 'n Sensoriese analise is uitgevoer om die eienskappe te vergelyk van Kefir geproduseer van massagekweekte korrels (MC), gevriesdroogde massagekweekte korrels wat gerehidreer en geaktiveer is (FDRA) en geaktiveerde massagekweekte korrels wat gevriesdroog en gerehidreed is (AFDR). Die chemiese samestelling van massagekweekte korrels (MC), massagekweekte, gevriesdroogde korrels (MCFD), massagekweekte, gevriesdroogde korrels wat gerehidreer en geaktiveer is (FDRA) en geaktiveerde massagekweekte korrels wat gevriesdroog en gerehidreer is (AFDR), is bepaal. Die optimum tydperk vir vriesdroging van korrels was 2 d en vir rehidrasie van gevriesdroogde korrels was 1 h. Die sensoriese analise het aangedui dat Kefir wat van FDRA en AFDR korrels geproduseer is, nie betekenisvol van mekaar verskil het nie, maar minder gefennenteerd was as Kefir wat van Me korrels geproduseer is. Die gevolgtrekking is gemaak dat 'n Kefirdrankie met uitstekende eienskappe geproduseer kan word met massagekweekte korrels. Vriesdroging is 'n beter metode as bevriesing om Kefirkorrels te preserveer a.g.v die ver1iesvan massa tydens bevriesing en die vergemakliking van vervoer en verspreiding van gevriesdroogde korrels. Die aanvulling van gevriesdroogde korrels met addisionele melksuurbakterieêen giste moet nog ondersoek word.

This dissertation investigated issues surrounding grain harvest and transportation logistics. A discrete event simulation model of grain transportation from the field to an on-farm storage facility was developed to evaluate how truck and driver resource constraints impact material flow efficiency, resource utilization, and system throughput. Harvest rate and in-field transportation were represented as a stochastic entity generation process, and service times associated with various material handling steps were represented by a combination of deterministic times and statistical distributions. The model was applied to data collected for three distinct harvest scenarios (18 total days). The observed number of deliveries was within ± 2 standard deviations of the simulation mean for 15 of the 18 input conditions examined, and on a daily basis, the median error between the simulated and observed deliveries was -4.1%. The model was expanded to simulate the whole harvest season and include temporary wet storage capacity and grain drying. Moisture content changes due to field dry down was modeled using weather data and grain equilibrium moisture content relationships and resulted in an RMSE of 0.73 pts. Dryer capacity and performance were accounted for by adjusting the specified dryer performance to the observed level of moisture removal and drying temperature. Dryer capacity was generally underpredicted, and large variations were found in the observed data. The expanded model matched the observed cumulative mass of grain delivered well and estimated the harvest would take one partial day longer than was observed. Usefulness of the model to evaluate both costs and system performance was demonstrated by conducting a sensitivity analysis and examining system changes for a hypothetical operation. A dry year and a slow drying crop had the largest impact on the system’s operating and drying costs (12.7% decrease and 10.8% increase, respectively). The impact of reducing the drying temperature to maintain quality in drying white corn had no impact on the combined drying and operating cost, but harvest took six days longer. The reduced drying capacity at lower temperatures resulted in more field drying which counteracted the reduced drying efficiency and increased field time. The sensitivity analysis demonstrated varied benefits of increased drying and transportation capacity based on how often these systems created a bottleneck in the operation. For some combinations of longer transportation times and higher harvest rates, increasing hauling and drying capacity could shorten the harvest window by a week or more at an increase in costs of less than $12 ha-1. An additional field study was conducted to examine corn harvest losses in Kentucky. Total losses for cooperator combines were found to be between 0.8%-2.4% of total yield (86 to 222 kg ha-1). On average, the combine head accounted for 66% of the measured losses, and the total losses were highly variable, with coefficients of variation ranging from 21.7% to 77.2%. Yield and harvest losses were monitored in a single field as the grain dried from 33.9% to 14.6%. There was no significant difference in the potential yield at any moisture level, and the observed yield and losses displayed little variation for moisture levels from 33.9% to 19.8%, with total losses less than 1% (82 to 130 kg dry matter ha-1). Large amounts of lodging occurred while the grain dried from 19.8% to 14.6%, which resulted in an 18.9% reduction in yield, and harvest losses in excess of 9%. Allowing the grain to field dry generally improved test weight and reduced mechanical damage, however, there was a trend of increased mold and other damage in prolonged field drying.

Orientador: João Domingos Biagi / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-04T08:37:02Z (GMT). No. of bitstreams: 1 Octaviani_JulioCesar_D.pdf: 4895521 bytes, checksum: 7f263de570a6e904ee68d3965a3297cc (MD5) Previous issue date: 2005 / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola

The objective of this research based on both the theory and experimentation was to prove that the total pressure difference is the primary driving force during the vacuum drying. The theoretical drying rates of diffusion, free water bulk flow and water vapor bulk flow were calculated and compared. The concept of equilibrium moisture content under the vacuum was developed. The theoretical maximum moisture content drop in one cycle was calculated using energy balance. The model was developed for the vacuum drying to understand the mechanism of the vacuum drying including the boiling front and its movement. To evaluate the effect of the sample size on the drying rate, four different thicknesses (1, 1.5, 2, 2.5 inches) and three different lengths (5, 10, 15 inches) were used. In the cyclic drying, the specimens were heated to the 60 C. The vacuum was pulled to about 18 mm Hg. The vacuum pump was kept running for 140 minutes. It was found that in cyclic vacuum drying, drying rate was not affected by the thickness. However, it was affected by the length. The cyclic drying curve consisted of two distinct parts. The fast drying period lasted about 10 to 20 minutes. The slow drying period occurred next when the pressure inside wood got close to the ambient pressure. In end grain vacuum drying, the specimens were coated with wax, wrapped in the plastic film and inserted into a rubber tube to prevent the moisture loss from the side surfaces during drying. The specimen size was 1×1×10 inches. Red oak and white oak were sealed and dried in both cyclic and continuous vacuum drying. The results showed that sealed specimens dried almost as fast as unsealed specimen. There was little moisture loss from the side surfaces. There was a moisture gradient along the length in both cyclic drying and continuous vacuum drying. Red oak specimens of 2.5×1.5×10 inches were used to study the boiling front in the vacuum drying. In order to detect the boiling phenomenon, the saturation pressures were calculated and were compared with the pressures at the same time and the same location. Boiling occurred during drying and the boiling front retreated to the center of wood as drying proceeded. The retreating speed depended on the heat supply and the permeability. Vacuum drying at room temperature was investigated. The specimens were dried at 20 C and pressure near 18 mm Hg. The results showed that wood can be vacuum dried at room temperature with little or no degrade at a reasonable drying rate. All experimental results support the objective of this study that the primary driving force is the total pressure difference. / Ph. D.

Orientadores: Marlene Rita de Queiroz, Thomaz Penteado de Freitas Borges / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-04T17:44:33Z (GMT). No. of bitstreams: 1 Santos_BrenoMonteirodos_M.pdf: 1088354 bytes, checksum: 34b6badc189dd2dfeafa1a3c5f41515c (MD5) Previous issue date: 2005 / Resumo: Uma metodologia para o projeto de coletores solares visando a secagem de grãos em silo foi implementada utilizando-se correlações empíricas previamente determinadas para o cálculo da fração solar fornecida pelo sistema. Foi realizado um estudo de caso de uma secagem de milho em silo, na cidade de Campinas ¿ SP, com pré-aquecimento do ar através de um coletor solar e aquecimento complementar com fonte energética convencional (GLP ou lenha). O coletor solar utilizado possui área de 1,80m2, foi construído com materiais de baixo custo e, devido ao material constituinte de seu leito (pedras britadas), apresenta elevada inércia térmica e capacidade de armazenar energia. A caracterização do coletor foi feita com o levantamento da sua curva de eficiência e com a determinação de sua constante de tempo. De maneira semelhante ao observado em coletores solares convencionais, a curva característica levantada apresentou comportamento linear. A capacidade de armazenar energia térmica foi constatada no elevado valor da constante de tempo obtida e pelas defasagens entre as curvas de calor útil fornecido ao ar e radiação solar incidente na superfície do equipamento. Na secagem de 1,20t de milho considerada no estudo de caso, utilizando-se uma vazão volumétrica específica de ar igual a 1,20 m3/m3.min à temperatura de 50°C, obteve-se uma economia de 31% na energia demandada para o aquecimento de ar. Através da análise de ciclo de vida econômico, para a utilização conjunta de energia solar e GLP no aquecimento de ar, foi determinada uma área coletora ótima de 7,50m2 a uma taxa de interesse de 0,12a.a., proporcionando o máximo retorno financeiro durante o ciclo de vida do equipamento. Aumentos nas taxas de interesse diminuem tanto os valores de área coletora ótima como do retorno financeiro durante o ciclo de vida econômico. Foi demonstrada, para as condições fixadas no estudo de caso, a viabilidade econômica da conversão de sistemas que utilizam GLP como fonte energética para sistemas assistidos por energia solar, proporcionando redução nos impactos ambientais da atividade e economia para o produtor rural. Nas mesmas condições foi verificada a inviabilidade econômica da utilização de energia solar em conjunto com a lenha / Abstract: A solar collector design procedure was proposed for sizing solar assisted crop-drying systems using empiric correlations, previously found, to determine the solar fraction supplied by the system. A case study of an in-bin crop drying was accomplished in the city of Campinas - SP with pre-heating of the air through a solar collector complemented by conventional energy source (LPG or firewood). The used solar collector had an area of 1,80m2, it was built with low cost materials and, due to its pebble bed, it presented a high thermal inertia and storing energy capacity. The collector was characterized by determining its efficiency curve and its time constant. As observed in conventional solar collectors, the characteristic curve presented linear behavior. The capacity to store thermal energy was confirmed by the high value of the time constant and by the delay between the useful heat and the incident solar radiation curves. In the studied case of drying 1,20 tons of corn, using a specific air flow rate equal to 1,20 m3/m3.min and a temperature of 50°C, it was saved 31% of the demanded energy for air heating. For a solar-assisted drying using LPG as the conventional source of energy, an optimum collector area of 7,50m2 was found through the life cycle saving analysis calculated with an annual interest rate of 0,12, providing the maximum saves during the equipment life cycle. Increasing the interest rate reduced both optimum collector areas and life cycle savings. For the crop drying case, it was demonstrated the economical viability of the conversion of LPG based to solar-assisted systems, providing reduction in the environmental impacts of the activity and savings for the rural producer. In the same conditions was demonstrated there is no economical viability in the conversion of firewood based to solar-assisted systems / Mestrado / Tecnologia Pós-Colheita / Mestre em Engenharia Agrícola

Made available in DSpace on 2014-08-20T13:44:35Z (GMT). No. of bitstreams: 1 dissertacao_victor_goltz.pdf: 3143568 bytes, checksum: bf72f21ec23b8d4e251915d335a9bf25 (MD5) Previous issue date: 2012-12-27 / The investment in reforestation with Eucalyptus as a way to ensure the cheap and quality supply of plant biomass to be used as an energy source in grain dryers, is constantly put into evidence in cereal companies and agricultural cooperatives. Like any other economic activity, needs to be assessed from the point of view of their financial return on invested capital, so that it can contribute to support the decisions. Thus, this study aims to analyze the economic feasibility for implementation of reforestation with eucalyptus to supply the needs of firewood in Seara Industria e Comercio de Produtos Agropecuarios Ltda in its three receiving, processing and storage plants installed in northern Parana. The calculation methodology took into consideration the needs of firewood annual production costs during the production cycle of 21 years , with cuts every 7 years, and considering that the price of wood is the one practiced by the regional market. To analyze the feasibility, we considered the assessment criteria for Net Present Value (NPV) and Internal Rate of Return (IRR) in two scenarios: a) considering the purchase area, b) considering the lease area. Both alternatives took into account areas far more than 150 km of consumer units. The opportunity cost considered was 6.0% per year. It was concluded that, investment in forestry as a source of biomass for energy, are economically feasible and provided the lease area required, being economically unfeasible scenario in purchasing the required area. / O investimento em reflorestamento com eucalipto, como forma de garantir o fornecimento de biomassa vegetal barata e de qualidade a ser utilizada como fonte de energia em fornalhas de secadores de grãos, é constantemente colocado em evidência em empresas cerealistas e cooperativas agrícolas. Assim como qualquer outra atividade econômica precisa ser avaliada do ponto de vista de sua retorno financeiro do capital investido, para que se possa embasar as decisões. Desta forma, este estudo visa analisar a viabilidade econômica para implantação de reflorestamento com eucalipto para suprir as necessidades de lenha da Seara Industria e Comercio de Produtos Agropecuários Ltda, em suas três unidade de recepção, beneficiamento e armazenamento instaladas na região norte do Paraná. A metodologia de calculo levou em consideração as necessidades de lenha anual, os custos de produção durante o ciclo de produção considerado de 21 anos, com cortes a cada 7 anos, e, considerando que o preço da lenha e aquele praticado pelo mercado regional. Para analise da viabilidade, foram considerados os critérios de avaliação pelo Valor Presente Liquido (VPL) e Taxa Interna de Retorno (TIR) em dois cenários: a) considerando a compra da área; b) considerando o arrendamento da área. Ambas alternativas levaram em consideração áreas distantes no máximo a 200 km das unidades consumidoras. A taxa mínima de atratividade considerada foi de 6,0% ao ano. Concluiu-se que o investimento em reflorestamento como fonte de biomassa vegetal para energia só e economicamente viável na condição de arrendamento da área necessária, sendo inviável economicamente no cenário de compra da área necessária.