The design of controllers for batch bioreactors

The implementation of control algorithms to batch bioreactors is often complicated by variations in process dynamics that occur during the course of fermentation. Such a wide operating range often renders the performance of fixed gain proportional-integral-differential (PID) controllers unsatisfactory. In this work, detailed studies on the control of batch fermentations are per formed. Two simple controller designs are presented with the intent to compensate for changing process dynamics. One design incorporates the concepts of static feedforward-feedback control. While this technique produces tighter control than feedback alone, it is not as successful as a controller based on gain scheduling. The gain-scheduling controller, a subclass of adaptive controllers, uses the oxygen uptake rate as an auxiliary variable to fine-tune the PID controller parameters. The control of oxygen tension in the bioreactor is used as a vehicle to convey the proposed ideas, analyses, and results. Simulation experiments indicate significant improvement in controller performance can be achieved by both of the proposed approaches even in the presence of measurement noise.     

The influence of different yeasts on the fermentation,composition and sensory quality of cachaça

Summary Cachaça (sugarcane wine) was produced using different yeast strains, six being strains of Saccharomyces cerevisiae and one each of Candida apicola, Hanseniaspora occidentalis, Pichia subpelliculosa and Schizosaccharomyces pombe. The ethanol yields (%) of the non-Saccharomyces strains were similar to those of the Saccharomyces strains. The following determinations were carried out on the cachaça: acetaldehyde, ethyl acetate, propanol, isobutyl alcohol, isoamyl alcohol, volatile acidity. The cachaças showed variations in the levels of secondary compounds, but these variations did not result in differences (P ≤ 0.05) in the sensory attributes of aroma and flavour and overall impression. Of the volatile compounds quantified in the cachaças, only propanol showed a positive correlation (P ≤ 0.05) with the flavour attributes and overall impression. The S. pombe strain was considered inadequate for the production of cachaça. The cachaças were classified into five groups in an exploratory Hierarchical Cluster Analysis as a function of the volatile compounds. Principal Component Analysis showed that 93% of the variation (PC 1) occurred among the samples, and was explained by the individual volatile compounds and the total secondary compounds, with the exception of isoamyl alcohol only 7% (PC 2) was associated with the volatile acidity. The negative correlations shown between the volatile compounds of the cachaças and the ethanol content of the sugarcane wine, with the exception of acetaldehyde, showed that the variation in ethanol content of the sugarcane wine is an important factor for standardization of the ethanol/volatiles ratio and the beverage quality.     

Taste quality changes as a function of salt concentration in single human taste papillae

Volume 4 number 1 p.8 Table I: In the column headed HCl (pH)50(3.60) should read 50(1.30)     

Taste quality changes as a function of salt concentration in single human taste papillae

A series of experiments were performed to determine whetherconcentration-dependent taste quality changes occur in simplesalt solutions when presentation of these solutions is restrictedto single fungiform taste papillae. Preliminary experiments,using small area, dorsal tongue stimulation, revealed the presenceof a sour-salty confusion in response to NaCl and HCl stimulation.This confusion was found to be greater at higher concentrationsand was affected by a pre-rinse. Taste quality changes as afunction of solution concentration for NaCl, KCl, and LiCl stimulationof single papillae were found to parallel those found previouslywith whole-mouth stimulation, although the sour component wasgreater at high concentrations, reflecting the effect of thepreviously identified sour-salty confusion. The data are discussedwithin the context of Dzendolet's (1968) physicochemical theoryof taste quality changes in salts. ^*This research was conducted as part of a thesis submitted inpartial fulfilment of the requirements for the degree of Doctorof Philosophy at the University of Massachusetts/Amherst. ^{* *}Current address: Behavioral Sciences Division, Food SciencesLaboratory, US Army Natick Research and Development Command,Natick, MA 01760, USA     

Taste profiles from single circumvallate papillae: comparison with fungiform profiles

Two experiments were conducted to investigate the psychophysicalresponse characteristics of single circumvallate papillae. InExperiment 1, 12 circumvallate papillae in four subjects werechemically stimulated to assess identification of taste qualities.Single circumvallate papillae were found to mediate multipletaste qualities, and the taste profiles obtained from differentpapillae were similar within the same subject. Moreover, sucrose,quinine monohydrochloride and citric acid elicited unitary andcharacteristic quality responding in these papillae from allsubjects, whereas NaCl elicited predominantly sour and/or bitterresponses from three of the four subjects. Experiment 2 directly compared responses obtained from singlecircumvallate papillae with those obtained from fungiform regionsof the tongue. Data for 10 subjects showed significantly greatersour responses to citric acid and NaCl in circumvallate papillaeand significantly greater salty responses to these compoundson the anterior tongue. In addition, the taste profiles forcitric acid and NaCl were distinct for circumvallate papillae,while those from the anterior tongue were similar. These datasuggest that the bitterness and sweetness of quinine and sugar,respectively, can be identified on the basis of sensory informationarising from either circumvallate or fungiform regions, butthat differentiation of the tastes of salts and acids may dependon a comparison of the input from both regions and/or additionalinformation arising from foliate regions.     

Tastes of salts and acids on circumvallate papillae and anterior tongue

In a psychophysical study with human subjects, three chloridesalts and three acids were tasted at two different isointenseconcentrations. Subjects profiled the taste sensations elicitedwhen the stimuli were applied to small regions of the anteriortongue and to individual circumvallate papillae. The resultsextended earlier findings showing systematic differences inthe responses to acids and salts as a function of the locusto which a stimulus is applied. All salts were perceived aspredominantly salty on the anterior tongue, and as predominantlysour or bitter on circumvallate papillae, although there wasa weak salty component in the response to lower concentrationsof salt on circumvallate papillae. Acids were perceived as souron circumvallate papillae, and as sour and salty on the anteriortongue. Cationic atomic weight was positively related to saltinesson both loci. However, while salts apparently stimulate bothbitter and sour receptors on both the anterior tongue and circumvallatepapillae, there was no systematic relationship between cationicatomic weight and the magnitude of the sour and bitter tasteselicited. It was concluded that the possibility of unequal distributionsof receptor types between fungiform and circumvallate regionsshould be taken into account when interpreting the results ofexperiments using whole-mouth stimulation with salts and acids. ¹This experiment was submitted as part of a dissertation bythe first author in partial fulfillment of the degree of Doctorof Philosophy at Brandeis University. The interpretations inthis paper are not to be construed as an official Departmentof the Army policy or position. ²Current address: Science and Advanced Technology Laboratory,US Army Natick Research and Development Laboratories, Natick,MA 01760.     

The taste, odor and hedonic quality of polyglycerols

Twenty subjects judged the taste and odor intensity and thetaste and odor pleasantness/unpleasantness of five concentrationsof sucrose, glycerol, a commercial triglycerol, a syntheticlinear diglycerol and a synthetic linear triglycerol. Judgmentsof intensity were made using the method of magnitude estimation;judgments of pleasantness/unpleasantness were made using a graphicline scale. Only the two linear polyglycerols had appreciableodor intensity. Both were described as having an ‘acrid’or ‘burnt caramel’ quality. The odor exponent forthe linear triglycerol was extremely high (1.44) and may beattributed to its intensely unpleasant quality. Sucrose wascharacterized solely by sweet taste, glycerol and the commercialtriglycerol by sweet and bitter tastes, the linear diglycerolby sweet, bitter and sour tastes, and the linear triglycerolby bitter and sour tastes. The relationships between perceivedtaste intensity and concentration were well described by powerfunctions, although the slope of the psychophysical functionfor the linear triglycerol was markedly lower than that forthe other compounds. The relative order of taste intensitieswas: linear triglycerol > sucrose > glycerol = lineardiglycerol > commercial triglycerol. Judgments of taste (andodor) pleasantness/unpleasantness showed only sucrose and glycerolto have positive hedonic qualities. All the polyglycerols werejudged unpleasant at all concentrations. Differences in thetaste and odor characteristics of the commercial and synthetictriglycerols were attributed to the commercial product beinga mixture of over 20 compounds. Although the synthetic lineardi- and triglycerols are effective in lowering water activity,these data suggest that more purified crystalline forms mustbe synthesized before they can be used effectively as humectantsfor intermediate moisture foods.