Effect of chemical and physical parameters on 2-acetyl-1-pyrroline production by Acremonium nigricans and its preservation by encapsulation | |
| Author | Muanmai Apintanapong |
| Call Number | AIT Diss. no.PH-00-2 |
| Subject(s) | Acremonium Microencapsulation--Preservation |
| Note | A dissertation submitted in pa1tial fulfillment of the requirements for the degree of Doctor of Technical Science. |
| Publisher | Asian Institute of Technology |
| Abstract | The production of 2-acetyl-1-pyrroline (ACPY), the main compound contributing to the fragrance of aromatic rice, by the fungi Acremonium nigricans, was investigated. The effect of chemical parameters (media composition and inorganic nitrogen source) on ACPY production was studied in shake flask fermentation. The physical parameters (such as aeration rate, agitation speed and pH control) and its kinetic study were determined in a 5 1 bioreactor. Encapsulation of ACPY with gum acacia and maltodextrin using the spray and freeze drying methods to retain aroma during storage was also conducted. Odor evaluation was done in the application of ACPY in milled rice. The volatile compounds of the culture broth of A. mgrzcans were extracted and analyzed by GLC and GLC-MS. A peak eluted at 5.43 min by GLC-MS gave the mass spectrum which was identical to that of ACPY from pandan leaf extracts and authentic compounds from chemical synthesis. From the Plackett-Burman statistical design, glucose gave a positive effect on ACPY production whereas potassium phosphate, biotin and Capantothenate were identified to have an inhibitory effect at the 60 % confidence level. The highest ACPY production was obtained from an optimized synthetic medium consisting of 20 mg/I biotin, 100 mg/l Ca-pantothenate, 300 mg/I pyridoxine.HCl, 400 mg/I thiamine, and 1000 mg/l inositol. The optimum concentrations of glucose, mono-potassium phosphate/dipotassium phosphate, and sodium chloride were 15, 1.27/0.1 and 0.25 g/l, respectively. The amount of ACPY obtained from this medium at 120 hours of cultivation was 3.45 mg/l. The culture media with ammonium nitrate and urea, as the inorganic nitrogen source, were observed to have high glucose consumption compared with media containing ammonium chloride. These inorganic nitrogen sources were not suitable precursors for ACPY production. In the 5 I bioreactor, the highest amount (3.06 mg/l) of ACPY was obtained at 0.875 vvm and 400 rpm with no pH control. From statistical analysis, aeration rate and agitation speed affected ACPY production. The effect of pH control at 0.875 vvm aeration rate and 300 rpm agitation speed was studied and the result showed that pH affected ACPY production. Cultivation of microorganisms at constant pH 4.5 yielded low concentrations of ACPY. Kinetic studies showed that specific growth rate, specific consumption rate, and product formation rate tended to increase with aeration rate and agitation speed. With constant pH of 4.5, maximum cell dry weight, specific growth rate, biomass yield coefficient, product yield coefficient, and product formation rate decreased. Substrate consumption rate at constant pH of 4.5 was higher than without pH control. For odor evaluation, the panelists used the term "pandan-like aroma" to describe ACPY from both pandan leaves and culture broth. More than 70 % of the panelists liked the odor from both samples. An odor threshold of 0.156 ppb of ACPY (from culture broth) in water was obtained from untrained panelists. Qualitative assessment of ACPY application in milled rice was then carried out. The samples with added ACPY from partially purified culture broth obtained a higher score for aromatic rice flavor than the control. However, overall acceptability was low. In ACPY encapsulation, spray-dried powders of 70:30 gum acacia-maltodextrin gave a minimum reduction of ACPY (27.7 %) after 72 days of storage. Freeze-dried powders from 70:30, 60:40, and 0:100 gum acacia-maltodextrin mixtures had no loss of ACPY within 60 days of storage. Under the scanning electron microscope, it was observed that increased ratios of gum acacia resulted in some deep dents on surfaces. The surfaces in all samples had no cracks or pores. Freeze-dried powders had complex forms and larger particles than spray-dried powders. In the humidification study, exposure of product powders to high relative humidity caused higher moisture contents and change in structure. High ratio maltodextrin powders formed a paste-like mass, whereas their moisture contents were lower. At high relative humidity, capsules were completely destroyed while freeze-dried powders were easily contaminated with microorganisms. The best ratio for encapsulation of ACPY was 70:30 gum acacia-maltodextrin mixture through freeze-drying because hygroscopicity was lower and ACPY was not lost. An odor evaluation of rice was conducted by adding encapsulated ACPY (70:30 gum acacia and maltodextrin) from partially purified culture broth to milled rice. The samples with encapsulated ACPY obtained a higher score for aromatic rice flavor than the control. Conversely, the overall acceptability obtained a low score. Some panelists commented that an off odor and lower overall acceptability might have been caused by the encapsulating materials (gum acacia and maltodextrin). |
| Year | 2000 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Postharvest and Food Process Engineering (PH) |
| Chairperson(s) | Athapol Noomhorm |
| Examination Committee(s) | Jindal, V .K.;Visavanathan, C. |
| Scholarship Donor(s) | Royal Thai Government |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2000 |