Optimization of preparation situations for immobilized yeast
Carbon supply optimization
The kind of carbon supply added has an impact on the scale of the immobilized yeast and the readability of the medium (Desk 3). The diameters of the immobilized yeast from massive to small have been lactose, glycerol, gluconic acid, glucose, and sucrose. On the identical time, the bigger the diameter, the smaller the variety of immobilized yeast. The carbon supply had no apparent impact on the floor state of the immobilized yeast, and the floor of the immobilized yeast with totally different carbon sources is clean. Nonetheless, totally different carbon sources had an impact on the readability of immobilized yeast tradition medium. When utilizing glucose, sucrose, and glycerol, the medium is cloudy as a result of the carbon supply used is appropriate for yeast progress11. Concurrently yeast overgrowth causes the medium to be cloudy and inhibits the expansion of P. chrysogenum. When lactose is used, the medium is yellow, whereas when gluconic acid is used, the medium is obvious and regular. Subsequently, contemplating the expansion state of immobilized yeast, gluconic acid is decided as the very best carbon supply.
Optimization of nitrogen supply
The kind of nitrogen supply added impacts the scale of the immobilized yeast and the floor state of the immobilized yeast (Desk 4). The diameters from massive to small are urea, peptone, yeast extract, (NH4)2SO4, KNO3. Per the impact of including totally different carbon sources on immobilized yeast, the bigger the diameter, the much less the variety of immobilized yeast. The immobilized yeast floor was tough when urea and peptone have been used, indicating that nitrogen sources might have an effect on the floor state of immobilized yeast. Primarily based on the diameter and floor state of immobilized yeast, yeast extract was decided as the very best nitrogen supply.
Optimum dosage of Penicillium chrysogenum spores
The mycelium of P. chrysogenum, because the provider of immobilized yeast, has a direct impression on the preparation of immobilized yeast12. The dimensions of the immobilized yeast is totally different as a result of totally different quantity of P. chrysogenum spores added are 6 × 104 cfu/ml > 1 × 105 cfu/ml > 6 × 105 cfu /ml > 1 × 106 cfu/ml > 6 × 106 cfu/ml (Desk 5). The addition quantity of P. chrysogenum can have an effect on the diameter and variety of immobilized yeast13. By way of the variety of immobilized yeasts, the extra P. chrysogenum spores are added, the extra immobilized yeasts can be. When the quantity of spores added is massive, extra spores can work together with the yeast in a unit quantity and may work together rapidly, so it’s simpler and sooner to type extra immobilized yeasts with small diameters. However, as a result of the variety of yeasts is mainly fixed, the extra spores of P. chrysogenum are added, the much less yeast could be successfully encapsulated by every immobilized yeast, and the quantity is small. The medium with every focus of P. chrysogenum spores was in a transparent state and the floor was clean, indicating that the addition of P. chrysogenum spores had no impact on the readability of the medium, that’s, the floor state of the immobilized yeast. Contemplating the amount and dimension of immobilized yeast, the optimum spore addition vary is 1 × 105 cfu/ml ~ 6 × 105 cfu/ml.
Orthogonal experiment
Primarily based on the above, it’s decided that the optimum carbon supply is gluconic acid, the optimum nitrogen supply is yeast extract, and the optimum addition quantity of P. chrysogenum spores is 1 × 105 cfu/ml ~ 6 × 105 cfu/ml. Orthogonal optimization of the preparation situations of immobilized yeast based mostly on the optimum carbon supply, nitrogen supply and the addition quantity of P. chrysogenum spores decided by single issue, design three-factor three-level orthogonal take a look at of things, the take a look at degree is proven in Desk 6.
The elements affecting the variety of encapsulated micro organism in immobilized yeast have been B > A > C, and the elements affecting the variety of leaking micro organism in immobilized yeast have been C > A > B. In keeping with the orthogonal outcomes (Desk 7), when the diameter is used as the choice customary, the optimum mixture is A2B2C1, specifically No. 5. When the variety of encapsulated micro organism is used as the choice criterion, the optimum mixture is A2B1C3, specifically No. 4. When the variety of leaking micro organism was used as the choice criterion, the optimum mixture was A2B2C1, specifically No. 5.
Results of mechanical energy of immobilized yeast
Immobilized yeast can be subjected to totally different mechanical forces throughout the fermentation course of, leading to crushing harm or scraping harm14, so the mechanical energy of immobilized yeast has an vital impression on the efficiency and repeatability of immobilized yeast. The 2 teams of optimum mixtures obtained from the optimized orthogonal take a look at of immobilized yeast, the take a look at teams No. 4 and No. 5, have been examined for mechanical energy (Fig. 1a,b). The comparability between the 2 was proven in Fig. 1c. It may be seen that the hardness of No. 4 is 0.105 N and the elasticity is 0.135 mm. The hardness of No. 5 is 1.29 occasions that of No. 4, and the elasticity is 1.5 occasions that of No. 4, that are 0.135 N and 0.207 mm, respectively.
(a) Texture map of the 4th group of immobilized yeast. (b) Texture map of the fifth group of immobilized yeast. (c) Hardness and springiness of immobilized yeast.
Subsequently, the optimum immobilized yeast was decided because the No. 5 take a look at group, with 5 g/L of gluconic acid, 5 g/L of yeast extract, and 1 × 105 cfu/ml of P. chrysogenum spores.
Comparability between immobilized yeast and free yeast
Comparability of fermentation efficiency
The outcomes of residual sugar and alcohol content material of crimson raspberry wine brewed by immobilized yeast and free yeast are proven in Fig. 2a,b. It may be seen that the residual sugar content material of free yeast is barely increased than that of immobilized yeast, and the sugar consumption fee of immobilized yeast is increased than that of free yeast, indicating that the fermentation fee of immobilized yeast is increased than that of free yeast.
(a) Comparability of residual sugar content material change between free yeast and immobilized yeast. (b) Comparability of alcohol content material between free yeast and immobilized yeast.
The alcohol content material of crimson raspberry wine brewed by immobilized yeast is 15% vol, and it brewed by free yeast is 14% vol. It was additionally proved that with the identical inoculum quantity, the fermentation capacity of immobilized yeast was higher than that of free yeast.
Comparability of substances in brewing crimson raspberry wine
The overall acid, anthocyanin, decreasing sugar and polyphenol content material of crimson raspberry wine brewed with immobilized yeast and free yeast have been analyzed.
It may be seen that the whole acid content material of the crimson raspberry wine brewed by immobilized yeast is 1.0438%, which is decrease than 1.3687% of the crimson raspberry wine brewed by free yeast (Fig. 3a). That’s, the acidity of crimson raspberry wine brewed by immobilized yeast is decrease than that of free yeast, and the style of crimson raspberry wine brewed by immobilized yeast can also be higher than that of free yeast.
(a) Comparability of acid worth between immobilized yeast and free yeast. (b) Comparability of anthocyanin content material between immobilized yeast and free yeast. (c) Comparability of decreasing sugar between free yeast and immobilized yeast. (d) Comparability of polyphenol content material between free yeast and immobilized yeast.
The anthocyanin content material of immobilized yeast brewed crimson raspberry wine was 111.604 mg/L, the decreasing sugar content material was 23.73 g/L, and the polyphenol content material was 565.67 mg/L; the crimson raspberry wine brewed by free yeast was 68.020 mg /L, 21.93 g/L, 395 mg/L respectively (Fig. 3b,c,d).The decreasing sugar content material of crimson raspberry wine brewed by free yeast and immobilized yeast has little distinction, however the content material of anthocyanins and polyphenols in immobilized yeast is increased. It exhibits that immobilized yeast can higher retain the lively elements of crimson raspberry wine in comparison with free yeast.
Comparability of aroma elements in brewing crimson raspberry wine
Figures 4 and 5 for the GC–MS whole ion efflux of aroma elements in immobilized yeast and free yeast fermented crimson raspberry wine. A complete of 40 important aroma elements have been detected within the two crimson raspberry wines, together with 5 alcohols, 21 lipids, 3 acids, 3 alkenes, 3 aldehydes and ketones, 1 phenol, and 4 others. The 2 crimson raspberry wines have the identical 22 sorts of aroma elements, primarily alcohols and esters.
GC–MS whole ion outflow Determine of aroma elements of crimson raspberry wine fermented with Immobilized yeast.
GC–MS whole ion outflow Determine of aroma elements of crimson raspberry wine fermented with free yeast.
It may be seen from Desk 8 that the primary aroma elements of the crimson raspberry wine brewed by immobilized yeast from excessive to low are isoamyl alcohol 6.8312%, isobutanol 2.8885%, ethyl acetate 2.7084%, isoamyl acetate 2.5946%, ethyl caprylate 2.0175%. The principle aroma elements of crimson raspberry wine brewed with free yeast from excessive to low are isoamyl alcohol 6.0499%, ethyl acetate 2.8018%, isobutanol 2.7780%, isoamyl acetate 2.0802%, ethyl caprylate 1.3425%.
Probably the most plentiful aroma element in each raspberry wines was isoamyl alcohol. The overall alcohol content material of crimson raspberry wine brewed by immobilized yeast was 11.3627%, which was increased than that of free yeast brewed crimson raspberry wine 10.6472%. The lipid content material of the crimson raspberry wine brewed with immobilized yeast was 10.0166%, which was increased than that of the crimson raspberry wine brewed with free yeast, which was 8.6791%. In contrast with free yeast fermentation (Fig. 6), immobilized yeast can considerably enhance the ester content material15. Different research have additionally proven that using immobilized yeast for fermentation can promote the manufacturing of aroma compounds reminiscent of alcohols and esters9. As well as, the immobilized yeast additionally successfully lowered the content material of risky acids, which was useful to the standard upkeep of crimson raspberry wine16.
Aroma composition of crimson raspberry wine fermented with Immobilized yeast or free yeast.
Steady fermentation efficiency of immobilized yeast
Determine 7a,b present the adjustments of residual sugar content material and alcohol content material of immobilized yeast for 3 consecutive fermentations. From the outcomes, the residual sugar content material of three consecutive fermentations was 9.5%, 10%, and 10.5%, respectively. Alcohol content material the levels have been 15% vol, 14.5% vol, and 14.2% vol. With the rise of fermentation occasions, the residual sugar content material elevated barely, and the alcohol content material decreased barely, however the adjustments weren’t apparent, indicating that the immobilized yeast of P. chrysogenum maintained good fermentation efficiency after three consecutive fermentations.
(a) Residual sugar change in steady fermentation of immobilized yeast. (b) Alcohol change in steady fermentation of immobilized yeast.
