Nestrukturirani modeli mliječno-kiselog vrenja

To describe a microbial process, two kinds of models can be developed, structured and unstructured models. Contrary to structured models, which take into account some basic aspects of cell structure, their function and composition, no physiological characterization of cells is considered in unstructured models, which only consider total cellular concentration. However, in spite of their simplicity, unstructured models have proven to accurately describe lactic acid fermentation in a wide range of experimental conditions and media. A partial link between cell growth and production, namely the Luedeking and Piret model, is mostly considered by the authors. Culture pH is the main parameter to be considered for model development. Acidic pH leads to inhibitory concentrations of undissociated lactic acid, the main inhibitory component, which causes cessation of growth and then production. On the other hand, pH control at optimal value for LAB growth allows to overcome product inhibition (by the total lactic acid produced or its undissociated part); hence nutritional limitations have to be considered for model development. Nitrogen is mainly involved in cessation of growth, owing to the fastidious nutritional requirements of LAB, while lactic acid production ceased when carbon was exhausted from the medium. The lack of substrate inhibition when usual concentrations of carbon substrate are used should be noted.Da bi se opisao mikrobni proces, upotijebljeni su strukturirani i nestrukturirani modeli. Strukturirani modeli uzimaju u obzir strukturu, funkciju i raspored stanica, a nestrukturirani ne uzimaju fiziološka svojstva, već samo ukupnu koncentraciju stanica. Ipak, usprkos njihovoj jednostavnosti, nestrukturirani modeli precizno opisuju mliječno-kiselo vrenje u različitim eksperimentalnim uvjetima i na raznim podlogama. Autori najčešće koriste Luedekingov i Piretov model, koji opisuje djelomičnu vezu između rasta stanica i proizvodnje mliječne kiseline. U razvoju ovoga modela najčešće je pH-vrijednost glavni parametar. Pri niskoj pH-vrijednosti nastaju inhibicijske koncentracije nedisocirane mliječne kiseline, što zaustavlja rast mliječno-kiselih bakterija, a time i proizvodnju mliječne kiseline. Taj se inhibicijski učinak može prevladati održavanjem optimalne pH-vrijednosti, ali pritom treba uzeti u obzir utjecaj hranjivih tvari na rast mliječno-kiselih bakterija. Nedostatak dušika je najčešći uzrok inhibicije mliječno-kiselih bakterija, jer im je prijeko potreban za rast, dok nakon iscrpljivanja ugljika iz podloge prestaje proizvodnja mliječne kiseline, što se može izbjeći korištenjem odgovarajućih koncentracija ugljika

Kinetic modelling of lactic acid production from whey

Thesis (Master)--Izmir Institute of Technology, Food Engineering, Izmir, 2004Includes bibliographical references (leaves: 59)Text in English; Abstract: Turkish and Englishxii, 75 leavesLactic acid is a natural organic acid, which is used in pharmaceuticals, chemical, textile and food industries. Since only L(+) lactic acid is found in normal human metabolism, the microbial production of L(+) lactic acid has great interest in recent years. Use of whey lactose to produce lactic acid by fermentation process is favourable due to the low cost of whey and its high organic matter content. Whey is suitable medium for some fermentations. However, its high lactose content makes it a potential environmental pollutant. The disposal problem of this pollutant could be overcome by utilization of whey lactose in the lactic acid production.The aim of this study was to develop a kinetic model for lactic acid productionfrom whey by Lactobacillus casei, which is a homofermentative lactic acid bacteria andcapable of producing L(+) lactic acid. Within this context, several batch fermentationexperiments in fermenter were performed at 37 C and pH 5.5. Seed culture that was produced in shake flask fermentations was used as the inoculum for the fermenter.Before the fermentation experiments, some of the proteins in whey were denatured by heat treatment and separated by centrifugation. This treatment decreased the protein amount from 11.15 % to 5.2 % in whey powder. The lactic acid production was associated with the biomass growth up to a certain time, but then a non-growth associated lactic acid production was observed in most of the fermentations except for the 9.0 g l-1 initial substrate fermentation run, where all the substrate was utilized when the stationary phase was attained. The maximum theoretical productivity was obtained as 2.4 g lactic acid l-1 h-1 in the fermentation with S0 equals to 35.5 g l-1. The kinetic parameters were obtained from different fermentation runs. mmax and KS were found as 0.265 h-1 and 0.72 g l-1, respectively. The average product yield coefficient, YPS, was determined as 0.682 g lactic acid (g lactose)-1.The modified form of logistic equation with product inhibition term for biomassThe modified form of logistic equation with product inhibition term for biomass growth, Luedeking and Piret equation for product formation and substrate utilization considering the consumption of substrate for product formation and maintenance, described most of the fermentation experiments in this study with high accuracy (SSE range was 0.0804-0.1531). The toxic powers in these inhibition terms, h and f, made the model applicable for the fermentation experiments with low and high initial substrate concentrations. In case of high initial substrate concentration fermentation (S0. 95.7 g l-1), the same model explains only the exponential phase of biomass and its product formation eventhough the substrate consumption is predicted very well.product formation eventhough the substrate consumption is predicted very well

Effect of different biopolymer-based structured systems on the survival of probiotic strains during storage and in vitro digestion

BACKGROUND: This study aimed to evaluate the protective effect of different biopolymer systems on the viability of two probiotics (Lactobacillus rhamnosus and Streptococcus thermophilus) during storage and in vitro digestion. Methylcellulose (MC), sodium alginate (SA), and whey protein (WP)-based structures were designed and characterized in terms of pH, rheological properties, and visual appearance. RESULTS: The results highlighted that the WP-system ensured probiotic protection during both storage and in vitro digestion. This result was attributed to a combined effect of the physical barrier offered by the protein gel network and whey proteins as a nutrient for microbes. On the other hand, surprisingly, the viscous methylcellulose-based system was able to guarantee good microbial viability during storage. However, this was not confirmed during in vitro digestion. The opposite results were obtained for sodium alginate beads. CONCLUSION: The results suggest that the capacity of a polymeric structure to protect probiotic bacteria is a combination of structural organization and system formulation. \ua9 2020 Society of Chemical Industry

Improved growth model for two-stage continuous cultures of Lactobacillus helveticus

An unstructured model for growth and lactic acid production during two-stage continuous cultures of Lactobacillus helveticus was previously developed. The Verlhust model was considered to describe growth kinetics. Production models was based on modified Luedeking-Piret expressions involving an inhibitory effect for the first stage (seed culture) and a nutritional limitation effect for the second stage (culture). To account for the decrease of the biomass concentration observed in the second stage, the dilution rate Dc was replaced by an exponential term of the dilution rate \u3b1 exp (Dc/\u3b2 ) in the growth and product relations. Contrarily to the previous model, the important decrease of the biomass concentration observed at steady state in the second stage at high dilution rates, namely close to wash out, was correctly described by the new model. It also proved to satisfactory describes production data and volumetric productivity

Cost-effective valorization of cassava fibrous waste into enantiomerically pure D-lactic acid: Process engineering and kinetic modeling approach

Cassava fibrous waste (CFW) valorization on the synthesis of D (-) lactic acid (DLA) holds enormous importance, particularly in the production of thermostable and biodegradable polymers. In this study, microbial kinetic modelling was carried out to investigate the dynamics of cassava fibrous waste enzyme hydrolysate (CFWEH) utilization towards DLA production. Designed biomass approach was attempted to evaluate the natural DLA producing organisms, capable of metabolizing CFWEH into optically pure DLA. Sporolactobacillus inulinus (NBRC 13595) was found to be the elite strain, resulting the yield of 99.43 % optically pure DLA using CFWEH-supplemented medium. Yeast extract (2 gL −1) was observed to be potential nitrogen source over other complex nitrogen sources for kinetic modelling investigation. Kinetic parameters predicted from the proposed model for DLA production showed maximum specific growth rate, - 0.36 (h−1); growth-associated product coefficient ( gg −1) and specific productivity ( gg −1h−1) respectively. Experimental data of biomass growth, substrate consumption and DLA production with initial sugar concentrations ranging from 20–180 gL −1 was found to be synchronized well with the simulated dynamic profiles. Kinetic investigation reported in this study is a novice attempt enumerating the valorization potential of CFW for the synthesis of value-added products including DLA at commercial scale in near future

Banana Nutrition

Banana Nutrition - Function and Processing Kinetics covers the nutritional aspects of the banana plant and fruit. The book contains substantial scientific information written in an easy-to-understand format. The chapters include information on pharmacological aspects of banana; banana bioactives: absorption, utilization, and health benefits; banana pseudo-stem fiber: preparation, characteristics, and applications; banana drying kinetics and technologies; and integrating text mining and network analysis for topic detection from published articles on banana sensory characteristics. All the chapters contain recent advances in science and technology regarding the banana that will appeal to farmers, plant breeders, food industry, investors, and consumers as well as students and researchers. Readers will harness valuable information about the banana in controlling food security and non-communicable nutrition-related human illnesses

Intensive propagation of the lactic acid bacterium Lactococcus lactis.

L.lactis is an important lactic acid bacterium, widely used in the dairy industry nowadays. The coccus is used as a natural acidifier for the inoculation of bulk quantities of milk in order to produce a variety of fermented products. As such, large quantities of its biomass are necessary. The possibility of producing the cellular biomass of the coccus in mass quantities was investigated through several techniques. Firstly, the bacterium was grown into simple batch cultures without pH control where the physicochemical needs of the coccus were determined. Through the determination of the optimum nutritional conditions for the propagation of the coccus, an optimised medium for growth occurred. The growth efficiency on the medium was tested on a 2L STR reactor operated batchwise with continuous pH control. The optimum pH conditions for the growth of the coccus were determined as well as parameters such as cellular yield coefficient, substrate and starter inoculum concentration. The metabolism o the coccus was determined as homofermentative, mainly producing lactic acid through measurements of the organic acids produced at the end of the fermentation process in the STR. In addition carbohydrate consumption rate in the optimum pH values selected was measure and the constant coefficients for substrate consumption end product inhibition effect and a maintenance coefficient term was determined. A simple mathematical model was constructed to describe the growth of the coccus batchwise and a correlation was made between the experimental data obtained from the STR fermentations and the theoretical predictions. An inhibition term was incorporated in the model in order to describe the inhibitory effect of lactic acid over the growth. With the use of the inhibition term a good fit between the experimental data and the model was obtained. The growth kinetics of L.lactis were further investigated by modelling its growth in a continuous system and in a Membrane Bioreactor system. The feasibility and the efficiency in all 3 systems was evaluated in terms of the volumetric cell productivity, (g/l/h). The models were also tested against different substrate concentrations, different starter inoculums, different dilution and flux rates. The MBR system has found to be highly productive especially when operated in the continuous mode of substrate feed, the volumetric cell productivity (g/l/h) (45.94 g/l/h) was over 10 times higher when compared with the volumetric cell productivity (g/l/h) given by the continuous system (1.4 g/l/h)and over 30 times when compared with the batch system(0.45 g/l/h). MBR was proven to be a possibly useful system for the development of high concentrations of cellular biomass but its practical application has to be further investigated