Purification of microbially produced Ca-L(+)-lactate with a novel technique: drying induced elution of impurities

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Gıda Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2016

Öğrenci: DAMLA ÖZÇELİK

Danışman: HALUK HAMAMCI

Özet:

For the production of calcium L-(+)-lactate (Ca-L(+)-Lactate) fermentation was performed by using Lactobacillus casei. Production with inexpensive raw materials and low cost purification of lactic acid (LA) as Ca-L(+)-Lactate was aimed because LA production from renewable materials is limited due to high production and purification costs. Fermentation conditions were 37°C for temperature, pH was kept at 5.5 by adding CaCO3 as neutralizer and stirring was adjusted at 120 rpm. Fermentation medium consisted of 7-10% carbohydrates from different substrates, 0-2.9% yeast extract and was supported by minerals and working volume of fermentation was 100 ml in small scale and 70 L for large scale. After fermentation was done solid particles were filtered off and the filtrate was evaporated to obtain 10% Ca-L(+)-Lactate. The color of the filtrate was light brown due to soluble proteins, trace metals and various other biochemical materials within. As an initial purification step, crystallization was done. The filtrate containing minimum 10% Ca-L(+)-Lactate was crystallized at 4°C and the crystals obtained were separated from liquid phase under vacuum. Nevertheless, the Ca-L(+)-Lactate cake obtained still had protein and trace metals in the inclusions. The cake was light yellow in color and the color deviation from white was treated as the impurity indicator since pure Ca-L(+)-Lactate is white in color. Its color difference from white was 267 ΔE in dry basis, it had still 0.1 g/L protein and 269 ppm Zn, 809 ppm Fe, 22 ppm Cu. Since the cake still had protein and trace metals further purification technique which is drying induced elution of impurities was experimented. Air flow rate and temperature were selected as 1 m/s and 55 °C and it had been observed that repeating more than four times of drying was unnecessary since there had been no further color change between bottom parts of samples. During drying part of purification step initial Ca-L(+)-Lactate had been 90.8 % in dry basis and became 98.3 % after four drying stages 90.2 % of the coloring compounds were removed. However, there was still 34 ppm protein, 97 ppm trace metals (Fe, Zn, Cu) and probably other undetermined materials in the final Ca-L(+)-Lactate powder.