Acidolysis and hot water extraction provide new insights into the composition of the induced "lignin-like" material from squash fruit.

Accumulation of "lignin-like" material (L-LM) by plant tissues in response to injury or disease has been observed in a wide variety of plant taxa. The most intensively studied L-LM is that produced by members of the Cucurbitaceae; this material is thought to be an unusual lignin rich in p-coumaryl alcohol derived subunits. Employing acidolysis we found the primary degradation product of L-LM from squash fruit was p-coumaryl aldehyde. These findings conflict with the current concept of L-LM, but would be consistent with L-LM being a polymer derived directly from p-coumaryl aldehyde or a gum containing this compound. Results of hot water extraction support the latter possibility. Further, we report on a simple TLC method useful for rapid qualitative characterization of acidolysis degradation products.

Squalene in grapefruit wax as a possible natural protectant against chilling injury.

The influence of temperature conditioning on stored grapefruit against chilling injury (CI) as related to the fruit's neutral lipids in the peel was investigated. Squalene, a highly unsaturated C30 isoprene hydrocarbon, was found to be present in the epicuticular wax of grapefruit. The optimal temperature for biosynthesis of squalene in grapefruit was 15°C; this is also the temperature reported previously as the optimum temperature for conditioning grapefruit against chilling injury. Control and temperature-conditioned grapefruit were stored monthly over three seasons from 1986 to 1989. Fruits were rated for chilling injury and the levels of squalene were determined. An inverse relationship found between CI and squalene level suggested that squalene may protect grapefruit from CI.

Rapid determination of double bond configuration and position along the hydrocarbon chain in cyclic fatty acid monomers.

This study reports the structural elucidation of diunsaturated 5- or 6-membered ring cyclic fatty acid monomers (CFAM) isolated from heated flaxseed oil by complementary gas chromatography (GC)-mass spectrometry (MS) and GC-matrix isolation-Fourier transform infrared spectroscopy (MI-FTIR). Infrared measurements of CFAM were carried out on methyl ester derivatives as well-resolved chromatograms were obtained on a polar 100% cyanopropyl polysiloxane capillary GC column. By contrast, electron ionization MS of methyl ester derivatives was of limited value because of double bond migration during the ionization process in the mass spectrometer. This communication reports definitive MS fragmentation patterns that can confirm ring position and double bond position along the fatty acid chain in 1,2-disubstituted CFAM determined as 2-alkenyl-4,4-dimethyl-oxazoline derivatives. Double bond configuration (cis, trans, or conjugated cis,cis) in CFAM was confirmed by GC-MI-FTIR. The presence of CFAM, degradation products found in used frying oils, is a potential source of dietary toxicity.

Identification of minor C18 triene and conjugated diene isomers in hydrogenated soybean oil and margarine by GC-MI-FT-IR spectroscopy.

Vegetable oils are partially hydrogenated in order to produce palatable products of suitable plasticity. The constituents of these new dietary products are complex mixtures of fatty acid isomers with different nutritional properties. A rapid method is described for separating and identifying fatty acid methyl ester (FAME) isomers of linolenic (octadecatrienoic, 18:3) acid and of conjugated octadecadienoic (18:2) acid, minor species found in hydrogenated soybean oil and margarine, by capillary gas chromatography-matrix isolation-Fourier transform-infrared (GC-MI-FT-IR) spectroscopy. FAMEs of 18:3 acid isomers in margarine, soybean oil hydrogenated in our laboratory, and isomerized linolenic acid were identified by this method, and MI-FT-IR spectra of FAME geometric isomers of octadecatrienoic and conjugated octadecadienoic acids are reported for the first time. Five major C18 triene GC peaks are found in chromatograms of isomerized methyl linolenate, representing species with tri-cis and tri-trans configurations and three species with cis-trans mixed configurations. FAME isomers with these configurations are also found for a hydrogenated soybean oil having an iodine value of 111. Methyl linolenate (tri-cis) is no longer found when soybean oil is further hydrogenated to an iodine value of 96. IR spectra characteristic of a tri-trans isomer are obtained for two test samples with iodine values of 111 and 96. Besides methyl linolenate, only isomers with a mono-trans di-cis configuration are found for the margarine analyzed. Conjugated cis-trans and trans-trans 18:2 FAME isomers are also found in all the hydrogenated soybean oil and margarine analyzed.

Activities by the schools to improve the distribution of dentists: an AADS report.

It appears that most dental schools have not yet become actively involved in efforts to solve maldistribution problems. However, there seems to be increasing interest in the potential benefits of extramural experience programs. Coordination of efforts by the schools, the state dental associations, and the state boards of dental examiners is very limited, but is clearly needed. Admissions committees seem to be trying to take into account the needs of rural areas and the inner city as well. Finally, the results of the survey point up the need for further study of these problems and of the value of particular approaches to them.

Use and application of structural models in dental education research.

The notion of prediction implies causation. Path and structural models explore the causal links rather than mere empirical relationships between variables. This technique involves a breakdown of correlations; it differs from correlation and regression methods in that it provides relevant information in the presence of important but unobserved (latent) explanatory variables and of measurement errors in the data. It also allows for more than one regression analysis simultaneously and affords inference through tests of the model. In this study, latent abilities of dental students were analyzed as causes and professional achievements as effects, with preadmission performances as indicators of latent abilities. A model with three constructs is consistent with the observed data. The results demonstrate that whereas correlation analysis presents limitations in interpretation, structural analysis focuses clearly on the direct impact of the quality of dental school education, rather than preadmission background, on clinical performance and board success as measures of future professional performance.

Professional performance among dental students: a factor analysis.

This study uses factor analysis of dental school performance to extract the underlying factors that are inherent in a set of a student's grades and to evaluate whether a given grade may be associated with more than one factor. Results suggest that overall performance is associated with factors that may be identified as basic science, dental science, and manual skill. The dental science factor appears to be developed during professional training and tends to be less clearly defined that the basic science and manual skills factors, respectively, the associations of clinical course grades with the defined factors are generally low, reflecting the complex involvement of dental clinic performance. It is reasonable to speculate, therefore, that dental school grades, when compounded together as overall GPA across the basic abilities of the students, constitute a likely source of variation that accounts for difficulties in prediction studies when they are used as criterion variables.

A derived basic ability criterion for predicting dental students' performance.

This study represents an attempt to develop a valid criterion for predicting students' performance while in dental school. Dental students' overall grade point averages were partitioned into component measures of relevant basic ability clusters in terms of factor scores. The derived indices were used as criterion variables in simple and multiple correlation and regression analyses, with Dental Admission Test (DAT) and predental college scores as predictors. Results showed that basic science abilities were associated with the preprofessional academic predictors, and manual skills with the DAT Perceptual Motor Ability Test (PMAT) scores. None of the presently available preprofessional predictors, taken singly or together, were correlated sufficiently with the factor-associated dental science performance or the nonfactor-associated dental clinical performance for effective prediction. Findings that the development of dental and clinical proficiency at the predoctoral level depends neither on available predictors nor on preprofessional background in the basic sciences have implications for traditional admission policies.

Accumulation of Putrescine during Chilling Injury of Fruits.

Putrescine (Put) increased 68% in lemon (Citrus limon (L.) Burm. f. cv Bearss) flavedo, 39% in grapefruit (C. paradisi Macf. cv Marsh) flavedo, 49% in grapefruit juice, and 149% in pepper (Capsicum annuum L. cv Early Calwonder) pericarp when fruits were stored at chilling temperatures. In lemon flavedo, the coefficient of correlation (r(2)) between Put concentration with severity of chilling was 0.90 and Put levels almost doubled; the injury index going from 1 to 2 units. Pepper pericarp, which was the most chilling-sensitive tissue tested (injury index going from 1 to 3.8 units), showed the greatest difference in Put accumulation (166 to 413 nanomoles per gram fresh weight) between storage temperatures of 7.2 and 1 degrees C. The least difference (338 to 470 nanomoles per gram fresh weight) was found in grapefruit flavedo between storage temperatures of 15.5 and 4.4 degrees C; the injury index going from 1 to 1.3 units.