Sunao Sato

An investigation of effect of replacing nitrate by urea in the growth and production of chlorophyll by Spirulina platensis

Abstract Chlorophyll is a pigment used as colorant in the food, pharmaceutical and cosmetic industries. It can be obtained in considerable quantities from Spirulina platensis biomass. In this work, the cultivation of the microalga was done using urea as the nitrogen source by a fed-batch process. The addition of urea was done in four different modes: intermittent addition every 24 or 48 h , continuous addition by exponentially increasing the added mass, and continuous addition by using a constant mass flow rate. The experiments were carried out at three different temperatures: 27° C , 30° C and 33° C and at a constant light intensity of 3.5 klx . The results showed a positive influence of urea in the growth of Spirulina but no effect on the final chlorophyll content of the cultures. Best results were obtained by continuous urea addition in exponentially increasing amount, at 30°C.

Effect of reducing the light intensity on the growth and production of chlorophyll by Spirulina platensis

Abstract The influence of light intensity reduction on Spirulina platensis cultivation was investigated, using urea and KNO 3 as nitrogen sources. The reduction of light intensity from 5 to 2 klux was studied both on the 9th and the 13th day of cultivation. Increases of up to 29% in the total chlorophyll production were observed for the cultivations with light intensity reduction, in comparison with the cultivations carried out at fixed light intensities.

Xylitol production by Candida guillermondii as an approach for the utilization of agroindustrial residues

Abstract Different substrates based on hydrolyzed hemicellulosic fractions of agroindustrial residues were used for xylitol production by Candida guilliermondii FTI 20037 under semi-aerobic conditions. Batch fermentation performances were characterized and compared with those attained in a synthetic medium using d -xylose as a major carbon source. For all media tested, simultaneous utilization of hemicellulosic sugars (glucose and xylose) was observed and the highest substrate uptake rate was attained in sugar cane bagasse medium. Increased xylitol concentrations (40 g/litre) were achieved in synthetic and rice straw-media, although the highest xylitol production rate was obtained in sugar cane bagasse hydrolysate. These results show that both hydrolysates can be converted into xylitol with satisfactory yields and productivities.

CULTIVATION OF ARTHROSPIRA (SPIRULINA) PLATENSIS (CYANOPHYCEAE) BY FED-BATCH ADDITION OF AMMONIUM CHLORIDE AT EXPONENTIALLY INCREASING FEEDING RATES†

Arthrospira (Spirulina) platensis (Nordstedt) Gomont was cultivated under light‐limited conditions in 5‐L open tanks by daily supplying NH4Cl as nitrogen source. Exponentially increasing feeding rates were adopted to prevent ammonia toxicity. The total feeding time (T) was varied between 12 and 20 days, and the starting (m0) and total (mT) quantities of the nitrogen source per unit reactor volume were varied in the ranges 0.19–1.7 mM and 2.3–23.1 mM, respectively. This intermittent addition of the nitrogen source prevented ammonia from reaching inhibitory levels and ensured final cell concentrations (Xm) and cell productivities (Px) comparable with those of batch runs with KNO3. Moreover, the lower nitrogen addition due to the use of NH4Cl rather than KNO3 allowed for higher nitrogen‐to‐cell conversions (Yx/n). These results were evaluated using three‐factor, five‐level, central composite experimental planning, combined with the response surface methodology, selecting T, m0, and mT as the independent variables and Xm, Px, and Yx/n as the response variables. This approach allowed us to identify, through the simultaneous optimization of the variables, T=16 days, m0=1.7 mM, and mT=21.5 mM as the best conditions for A. platensis cultivation at 72 μmol photons·m−2·s−1. Under these conditions, a maximum cell concentration of 1239 mg ·L−1 was obtained, which is a value comparable with that obtained using KNO3 as nitrogen source and nearly coincident with the theoretical one estimated by the response surface methodology.

Influence of media composition on xylitol fermentation by Candida guiliiermondii using response surface methodology

SummaryThe bioconversion of xylose to xylitol by the yeast Candida guilliermondii FTI 20037 was evaluated under different nutritional conditions using rice straw hemicellulose hydrolysate. Statistical designs were used to determine the fermentation medium composition. Ammonium sulfate and rice bran have been identified as required nutrients in the hydrolysate since there was a significant interaction between them. In the presence of both nutrients, the xylitol yield factor (Yp/s) and volumetric productivities (Qp) were 0.68 g/g and 0.54 g/L.h, respectively.

Evaluation of rice straw hemicellulose hydrolysate in the production of xylitol byCandida guilliermondii

SummaryRice straw was used as a lignocellulosic source to provide rich pentose media. By using a well characterized yeast strain,Candida guilliermondii FTI 20037, the hydrolysate obtained was converted to xylitol with an efficiency of 75% and production of 27 g of xylitol per liter in 48 hours. The satisfactory results reported here can be attributed to the low concentrations of toxic components generated throughout the chemical depolymerization of this raw material.

Fed-batch cultivation of Arthrospira (Spirulina) platensis: potassium nitrate and ammonium chloride as simultaneous nitrogen sources.

Arthrospiraplatensis was cultivated in minitanks at 13 klux, using a mixture of KNO(3) and NH(4)Cl as nitrogen source. Fed-batch daily supply of NH(4)Cl at exponentially-increasing feeding rate allowed preventing ammonia toxicity and nitrogen deficiency, providing high maximum cell concentration (X(m)) and high-quality biomass (21.85 mg chlorophyll g cells(-1); 20.5% lipids; 49.8% proteins). A central composite design combined to response surface methodology was utilized to determine the relationships between responses (X(m), cell productivity and nitrogen-to-cell conversion factor) and independent variables (KNO(3) and NH(4)Cl concentrations). Under optimum conditions (15.5mM KNO(3); 14.1mM NH(4)Cl), X(m) was 4327 mg L(-1), a value almost coincident with that obtained with only 25.4mM KNO(3), but more than twice that obtained with 21.5mM NH(4)Cl. A 30%-reduction of culture medium cost can be estimated when compared to KNO(3)-batch runs, thus behaving as a cheap alternative for the commercial production of this cyanobacterium.

Effect of inoculum level on xylitol production from rice straw hemicellulose hydrolysate byCandida guilliermondii

The effect of inoculum level on xylitol production byCandida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate. High initial cell density did not show a positive effect in this bioconversion since increasing the initial cell density from 0.67 g L−1 to 2.41 g L−1 decreased both the rate of xylose utilization and xylitol accumulation. The maximum xylitol yield (0.71 g g−1) and volumetric productivity (0.56 g L−1 h−1) were reached with an inoculum level of 0.9 g L−1. These results show that under appropriate inoculum conditions rice straw hemicellulose hydrolysate can be converted into xylitol by the yeastC. guilliermondii with efficiency values as high as 77% of the theoretical maximum.

Influence of kLa on bioconversion of rice straw hemicellulose hydrolysate to xylitol

Abstract The effect of overall oxygen mass transfer coefficient (kLa) on the conversion of xylose to xylitol by Candida guilliermondii FTI 20037 was investigated in batch experiments. Rice straw hemicellulose hydrolysate obtained by acid hydrolysis was employed as a xylose-rich medium. The results showed that this bioconversion strongly depended on the aeration rate. The maximum volumetric productivity (0.52 g/l h−1) and the highest xylitol yield (0.73 g/g) were achieved at an overall oxygen mass transfer coefficient of 15 h−1. Under these conditions 80% efficiency in relation to theoretical yield was attained.

Ethanol production by Saccharomyces cerevisiae grown in sugarcane blackstrap molasses through a fed-batch process: optimization by response surface methodology.

We studied the effect of reactor filling time (T) (3–5 h), initial mass of inoculum (M) (1000–2100 g), and exponential time decay constant for the substrate feed rate (K) (0.6–1.6 h−1) on ethanol production by Saccharomyces cerevisiae grown in sugarcane blackstrap molasses through a fed-batch culture. The highest ethanol productivity (16.9 g/[L·h]) occurred at T=3h, K=1.6 h−1, and M=1300 g. In addition, productivity was affected by both M (for T=3 and 4 h) and K (for T=3 h) and varied inversely with T under any value fixed for M and K. By the quadratic regression multivariable analysis method, equations were determined to estimate ethanol yield and productivity as function of the variables studied (T, K, and M).