Selection and characterization of mixed starter cultures for lactic acid fermentation of carrot, cabbage, beet and onion vegetable mixtures.

An evaluation of various lactic acid bacteria (LAB) for the fermentation of cabbage, carrot and beet-based vegetable products was carried out. As part of a screening process, the growth of 15 cultures in a vegetable juice medium (VJM) was characterized by automated spectrophotometry. Acidification patterns as well as viability during storage of the LAB were also established. There were greater differences between the pure cultures than the mixed ones with respect to growth in VJM and viability during storage. Reductions in viable cell counts during storage of the fermented VJM occurred more rapidly with a Leuconostoc strain than for pediococci or lactobacilli. Inoculation of vegetables was carried out with cultures of Lactobacillus plantarum NK-312, Pediococcus acidilactici AFERM 772 and Leuconostoc mesenteroides BLAC which were rehydrated in a brine. This rehydration procedure was not detrimental to viability. During fermentation of a carrot/cabbage vegetable mix, sugar metabolism was characterized by the assimilation of both glucose and fructose, but sugars remained in the fermented vegetables when acidification stopped. The pH in the LAB-inoculated vegetables after 72 h at 20 degrees C was significantly lower (by 0.2 units) than the uninoculated control. Inoculation with LAB designed for silage fermentation resulted in the inhibition of acetic acid production, and reduced the production of ethanol during fermentation. The selection process on VJM enabled the preparation of a mixed culture that was more rapid than the silage inoculants in acidifying the medium and was more effective in reducing the production of gas during the fermentation and storage of the fermented vegetables.

Contribution of area 17 to cell responses in the striate-recipient zone of the cat's lateral posterior-pulvinar complex.

The cat's lateral posterior-pulvinar complex (LP-pulvinar) contains three main representations of the visual field. The lateral part of the LP nucleus (LPl or striate-recipient zone) is the only region of these extrageniculate nuclei which receives afferents from the primary visual cortex. We investigated the contribution of area 17 to the response properties (orientation and spatial frequency tuning functions) of LPl neurons by cooling or lesioning the visual cortex. Responses of 40 LPl cells were studied before, during and after the reversible cooling of the striate cortex. When tested for orientation, a total of 10 units out of 28 was affected (36%). For most of these cells (eight of 10), cooling the visual cortex yielded a reduction of the cells' visual responses without altering their orientation-selectivity (there was no significant change in the orientation tuning width). For only two cells, inactivation led to an increase in the response amplitude. Also, blocking the visual cortex never modified the direction-selectivity of LPl cells. When tested for spatial frequency, 12 neurons out of 33 were affected (36%) by the experimental protocol. In most cases, we observed a reduction in the responses at each spatial frequency tested, with no change in tuning bandwidth. For only three LPl cells, the effects of inactivation of the visual cortex were restricted to specific spatial frequencies, altering the profile of the spatial frequency tuning function. In five cats, removing area 17 reduced the proportion of visual neurons in LPl and the spared visually evoked responses were noticeably depressed. Despite the reduction in responsiveness, a few LPl receptive fields within the cortical scotoma were still sensitive to the orientation and/or direction of a moving stimulus. This last observation suggests that some properties in LPl could be generated either by circuits intrinsic to the LPl or by afferents from extrastriate cortical areas. Overall, these results indicate that projections from the visual cortex to the striate-recipient zone of the LP-pulvinar complex are mainly excitatory. Despite the strong impact of the area 17 projections, our data suggest that the extrastriate cortex could also play a role in the establishment of response properties in the cat's LPl.

Responses to moving texture patterns of cells in the striate-recipient zone of the cat's lateral posterior-pulvinar complex.

We have studied the response properties of cells in the lateral part of the lateral posterior nucleus or striate-recipient zone (LPl) of the lateral posterior nucleus-pulvinar complex to the motion of textured patterns [visual noise]. Our purpose was to determine basic noise response characteristics and to compare these properties to that of cells in area 17 known to project to the LPl. Practically all LPl cells (87%) responded to the motion of visual noise. The evoked discharges were either sustained or characterized by several bursts. On average, as found in cortex, LPl neurons were more broadly tuned for the direction of noise than that of gratings (bandwidths of 49 and 36 degrees, respectively; t-test, P < 0.005). Noise tuning function in LPl was comparable to that found in cortex (mean of 48 degrees). One third of the LPl units did not exhibit any preferences for drift direction of noise. Such cells were virtually not encountered in the striate cortex. This group of LPl cells was generally not tuned for grating direction. For practically all LPl cells, responses to noise varied as a function of drift velocity. The mean optimal velocity was 27.5 degrees/s with mean bandwidth of 2.5 octaves. LPl cells were sensitive to a broader range of velocities than complex cells in area 17. The results of the present study showed that visual noise is an appropriate stimulus for studying motion sensitivity of cells in the LPl. It also revealed that the noise response properties, such as direction and velocity tuning functions, are very similar to those reported in the striate cortex. The exact contribution of area 17 in the visual noise responsiveness of LPl cells remains to be determined. This study provides additional evidence that the lateral posterior nucleus-pulvinar complex may be involved in many aspects of visual processing.

Motion sensitivity and stimulus interactions in the striate-recipient zone of the cat's lateral posterior-pulvinar complex.

The cat's lateral posterior-pulvinar complex (LP-pulvinar) establishes reciprocal connections with the anterior ectosylvian visual (AEV) and lateral suprasylvian (LS) cortices; two regions which are believed to be involved in motion analysis. We have investigated the motion sensitivity of neurons in the LP-pulvinar complex by: (1) studying the responses properties of cells in the striate-recipient zone of the LP nucleus (LPI) to the drift of a two-dimensional texture pattern (visual noise); and (2) determining the extent to which the latter stimulus can modify the spatial frequency tuning function of LPI cells. Experiments were carried out on anesthetized normal adult cats. Almost all LPI cells (55 out of 63, 87%) responded to the motion of visual noise. For most units (39 out of 55, 71%), responses varied as a function of the direction of motion (bandwidth of 49 degrees). One-third of the LPI units did not exhibit any preference for drift direction of noise. For practically all LPI cells, responses to noise varied as a function of drift velocity. Optimal velocities were distributed from 2 to 35 degrees/s with a mean value of 27.5 degrees/s (means bandwidth of 2.5 octaves). The influence of visual noise on the spatial frequency tuning function of 22 LPI cells was also studied. For half of LPI cells, responses at all spatial frequencies were reduced when the grating and the texture pattern were moving in opposite directions (anti phase condition). This masking effect of noise was rarely observed when both stimuli were drifted in the same direction (in phase condition). These results suggest that the LP-pulvinar complex may be part of extrageniculate pathways involved in the analysis of motion of visual targets and/or the analysis of the relative movement between an object and its surrounding environment.

Comparison of the responses to moving texture patterns of simple and complex cells in the cat's area 17.

1. Whether complex (C) cells are the only truly texture-sensitive units in the cat's primary visual cortex remains controversial. In view of the strong physiological significance of having putatively only one class of cells sensitive to visual noise in the striate cortex, we reinvestigated this issue. Sensitivities of simple (S) and C cells to noise were quantitatively studied and compared in order to clearly document the response properties of cells in the striate cortex to visual noise and to establish whether one can unequivocally segregate S from C cells on the basis of those specific properties. 2. Receptive fields were stimulated with all relevant stimuli, i.e., drifting sine-wave gratings, electronically generated noise pattern of 256 x 256 elements (ratio 1:1 of dark and light elements), and flashing and moving bars (both bright and dark). 3. A total of 60 S cells out of 85 (70.6%) and 90 C cells out of 101 (81.8%) responded to the motion of visual noise. Responses of most C cells were sustained, i.e., their discharge rate was maintained at a constant level throughout presentation of the stimulus. On the other hand, responses of the majority of S cells were characterized by several bursts of discharges. On average, optimal firing rates were greater for gratings than for noise. 4. For practically all cells, responses to noise varied as a function of direction of motion. The mean direction bandwidths were, respectively, 43 +/- 24 degrees and 48 +/- 23 degrees (mean +/- SD) for S and C cells. In both groups, neurons were more broadly tuned for the direction of noise than that of gratings (t-test, P < 0.001). We rarely observed bimodal tuning curves for noise, with each peak lying on either side of the orientation curve. These results could be expected if one considers texture stimuli not in the space domain (as dot patterns) but in the frequency domain, i.e., patterns containing all spatial frequencies and orientations. 5. In general, the direction indexes of S and C cells were similar whether they were stimulated by drifting noise or gratings. S cells had a slight tendency to be more direction selective for noise than for gratings. 6. For all S and C cells tested, responses to noise varied as a function of drift velocity. The mean optimal velocity was 12.9 and 10.2 degrees/s for S and C cells, respectively (t-test, P > 0.05). Most cells were band-pass with mean bandwidths of 2.2 and 2.7 octaves for S and C cells, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)