Vegetable Leather Research Articles

Physical, Chemical, Sensory and Microbiological Attributes of Sweet Potato Leather

ABSTRACTA “vegetable leather,” possessing a supple, leathery texture, was prepared with sweet potato (SP) and other ingredients. Samples were analyzed at 0, 30, and 60 days storage. Texture, but not flavor or acceptance, was affected by experimental factors. Ingredients had only minor effects on composition. Mean values were: moisture, 5.9%; crude protein, 5.8%; crude fat, 4.9%; ash, 2.7%; crude fiber, 2.2%; and nitrogen‐free extract, 84.8%. Dietary fiber was 4.1%. Color of the leather was orange; pH was 4.8; annd caloric content was 17.3 kJ per g. Water activity ranged from 0.48 for leather with SP and apple to 0.58 for leather with SP and without apple. Microbiological counts of samples were low.

Influence of temperature and moisture on the electrical properties of leather

Apparent, or bulk, dielectric constants and power factors of chrome and vegetable leather and untanned hide are reported for moisture contents up to 30 percent, at tempera­ tures of 23° C, 0° C, and —70° C over the frequency range 0.75 to 96 kilocycles. Dielectric constants of fibers determined on dry material at 3 kilocycles and 22° C are: chrome 5.4; vegetable 6.4; and kangaroo tendon 5.1. Apparent direct-current resistivity decreases from values >1016 ohm-cm when dry to values <109 ohm-cm at 30-percent moisture. Apparent dielectric decreases with frequency and temperature at all moisture contents, the frequency dependence increasing with moisture content. Apparent power factors generally exhibit similar behavior. At —70° C at high moisture contents, a diffuse absorption maxi­ mum observed may be due to ice or to permanent dipoles of collagen which are freed by moisture. Observed behavior is interpreted as probably arising from a combination of interfacial polarization at surfaces existing in the fibrous leather and dipolar polarization. Results indicate electrical measurements in this frequency range are probably not reliable for precise quantitative moisture analyses. Adsorption of moisture by hygroscopic materials generally causes a marked change in the electrical properties (conductivity, dielectric constant, and power factor) of such substances. This effect is gen­ erally attributed to the high dielectric and conductivity of the adsorbed moisture as compared to the much lower values exhibited by the dry adsorbate. In view of the large electrical effects pro­ duced by the moisture and the rapidity, relative sim­ plicity, and nondestructive nature of electrical meas­ urements, such determinations have been proposed as methods for quantitative moisture determinations [3, 14, 41].* Unfortunately, the materials of par­ ticular interest in this connection are usually powders or fibrous materials that possess large adsorption surface areas and, therefore, the results of electrical measurements are not easily interpreted because of the complex physical structure of the specimens. Recently, interest has arisen in application of dielec­ tric measurements for the determination of moisture in leather [27]. This report describes the results of critical studies of the effects of moisture and temperature on the dielectric and power factor of leather in the audio and low intermediate frequency range. In most measurements dealing with a porous mate­ rial such as leather, two experimental values are recognized, a value associated with the fibers alone, and an apparent value that refers to the bulk material including the air in the interstices. To avoid confusion between the former and the real part of the complex dielectric constant, the term fiber dielectric constant will be used instead. Apparent values as used are understood to refer to the bulk material.