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Based on MRS medium, two types of food grade (FG) culture media (FG medium I and FG medium II) for the preparation of a concentrated starter culture of Lactobacillus plantarum NRIC 0380 to manufacture a new type of instant Chinese noodle, the fermented instant Chinese noodle, were developed using FG materials. FG medium I, which is for normal static culture, contains table sugar (sucrose), Yeast peptone standard type F, Sunsoft Q-17S (emulsifier), sodium acetate, trisodium citrate and MnSO 4 · 4-5H 2 O. FG medium II was designed to be used for the pHcontrolled jar fermentor culture conditions. Therefore, sodium acetate and trisodium citrate as a buffer to prevent acidification of medium were omitted from FG medium I. When L. plantarum NRIC 0380 was cultured under the pH-controlled jar fermentor culture conditions, the kinetics of growth, sugar consumption and lactic acid production in FG medium II were quite similar to those observed in the Difco Lactobacilli MRS Broth. Furthermore, growths of many lactobacilli strains isolated from various fermented foods in FG medium I were also quite similar to those observed in MRS medium. Therefore, simple and practical FG media for the culture of lactobacilli were successfully established.

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We determined the maximum pH that allows growth (pHmax) for 34 strains of lactobacilli. High alkali tolerance was exhibited by strains of Lactobacillus casei, L. paracasei subsp. tolerans, L. paracasei subsp. paracasei, L. curvatus, L. pentosus, and L. plantarum that originated from plant material, with pHmax values between 8.5 and 8.9. Among these, L. casei NRIC 1917 and L. paracasei subsp. tolerans NRIC 1940 showed the highest pHmax, at 8.9. Digestive tract isolates of L. gasseri, L. johnsonii, L. reuteri, L. salivarius subsp. salicinius, and L. salivarius subsp. salivarius exhibited moderate alkali tolerance, with pHmax values between 8.1 and 8.5. Dairy isolates of L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis, and L. helveticus exhibited no alkali tolerance, with pHmax values between 6.7 and 7.1. Measurement of the internal pH of representative strains revealed the formation of transmembrane proton gradients (⌬pH) in a reversed direction (i.e., acidic interior) at alkaline external-pH ranges, regardless of their degrees of alkali tolerance. Thus, the reversed ⌬pH did not determine alkali tolerance diversity. However, the ⌬pH contributed to alkali tolerance, as the pHmax values of several strains decreased with the addition of nigericin, which dissipates ⌬pH. Although neutral external-pH values resulted in the highest glycolysis activity in the presence of nigericin regardless of alkali tolerance, substantial glucose utilization was still detected in the alkali-tolerant strains, even in a pH range of between 8.0 and 8.5, at which the remaining strains lost most activity. Therefore, the alkali tolerance of glycolysis reactions contributes greatly to the determination of alkali tolerance diversity.Lactic acid bacteria (LAB) produce lactic acid as a main product of sugar fermentation. Many studies have examined the response of LAB to acid stress, including the mechanisms underlying acid tolerance (3,4,28). In contrast, very few studies have examined the stress response of LAB to alkaline environments. Several alkali-tolerant/alkaliphilic LAB, which are capable of growing at pH values of Ͼ9.5 as well as producing large amounts of lactic acid from glucose, have been reported to date: Enterococcus hirae (formerly Streptococcus faecalis) (8), Pediococcus urinaeequi (23), Alkalibacterium olivapovliticus (12, 24), Marinilactibacillus psychrotolerans (12), M. piezotolerans (27), Halolactibacillus halophilus, and H. miurensis (13).The mechanism underlying the alkali tolerance of LAB has been examined in E. hirae ATCC 9790T . Biochemical experiments and mutant analyses suggest that E. hirae ATCC 9790 T maintains an internal pH lower than the external pH by the operation of an ATP-driven K ϩ /H ϩ antiporter during growth at an external pH of around 9.5 (14-17). However, E. hirae ATCC 9790T has no such system to maintain a near-neutral internal pH in an alkaline medium (22). Thus, the contribution of internal-pH maintenance to alkali tolerance in this bacterium is controversial. Adaptation to alkaline stre...

The lactic acid fermentation of instant Chinese noodle sheet by Lactobacillus plantarum NRIC 0380 changed the noodle quality as evaluated by texture and sensory tests. This interesting change was induced by only a short 2-h fermentation time, however the noodle quality subsequently degraded with prolongation of the fermentation of up to 24 h. SDS-PAGE analysis of proteins in the noodle sheet indicated no change in proteins extracted from the 2-h fermented noodle sheet compared to non-fermented noodle sheet. In contrast, native-PAGE analysis showed a shift in molecular weight of gluten proteins, with those extracted from the 2-h fermented noodle sheet having a higher molecular weight than those from nonfermented noodle sheet. These results strongly suggested a conformational change of gluten proteins in the noodle sheet caused by the short 2-h fermentation. The 2-h lactic acid fermentation decreased the pH from 8.5 to 7.5, but gluten proteins extracted from noodle sheet made with the addition of lactic acid to adjust the pH to 7.3 did not show this increase in molecular weight. Thus, the change from native state of gluten proteins does not seem to be induced by the presence of the lactic acid itself but by other factor(s) associated with lactic acid fermentation. On the other hand, the reduction of noodle quality by prolonged fermentation for up to 24 h seems to induce degradation of albumin and globulin proteins as revealed by SDS-PAGE analysis and also the change in the native state of gluten proteins as detected by native-PAGE analysis.

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