No abstract

Commercial canning of freestone peaches, such as Elbertas, often results in tissue sloughing and a ragged appearance by comparison with the firmly coherent texture of canned clingstone varieties. In some areas, however, plantings of freestone varieties predominate and have increased to the point that quality improvement in their use in the canned fruit market has received serious consideration. This is the situation in the state of Washington (10) where it has been found that the canning quality of Elberta peaches can be improved by orchard application of high levels of nitrogenrich fertilizers (5,13).Quality requirements for canned freestone peaches differ from those for market of the fresh fruit. The influence of nitrogen on tree growth and on yield and quality of the fresh fruit have been generally recognized at least since 1930-1931 described in detail the composition and fresh fruit qualities of high and low nitrogen, New Jersey -grown Elberta and Shipper Cling peaches. These authors considered that the high nitrogen Elberta fruit did not develop a desirable flesh color until too soft for shipment and table use. Peaches representing low to medium nitrogen levels, however, tended to be slightly elongate in shape, matured and colored more rapidly, and could be harvested earlier at a firmer texture for shipment. In general, it has been recognized that trees of high nitrogen nutrition show lush, vigorous growth and bear larger, more rounded fruit than do low nitrogen trees which have comparatively sparse growth and smaller leaves. Very similar differences in fresh fruit qualities were found by Carter et aZ. between Elberta peaches from trees of high and low levels of applied nitrogen grown in soil management plots in Washington State (5,13).However, fruit from trees receiving applied nitrogen fertilizers in amounts necessary for maximum yields was considered to be superior in canning qualities to that representing low to deficient nitrogen conditions. When canned, the high nitrogen fruit showed a firm, finely coherent texture, good color, and was less astringent that the coarse, often stringy and ragged fruit from trees of low nitrogen status.The fine and coherent versus the coarse and ragged texture of these canned Elberta peaches suggested that cellular distinctions may result from different levels of applied nitrogen. The possibility was investigated and comparative histological studies were made on selected samples of these Washington State peaches in both the canned and the fresh conditions.

In the synthesis of a series of regular polyampholytes,' copolymers of 3,6-diallyl-2-piperidone and a,w-dithiols were hydrolyzed with dilute sulfuric acid to open the piperidone ring; this was followed by neutralization of the acid with sodium hydroxide to yield the polyampholyte:The residual sodium sulfate proved to be difficult to remove. Such inorganic salts and other low molecular weight impurities are commonly removed from aqueous protein solutions by dialysis through a semipermeable membrane.z Dialysis against distilled water with the polyampholyte encased in seamless cellulose dialyser tubing (1.25 in.) was not effective for removing residues of around 1% which we had not been able to remove by washing. We found, however, that dialysis was accomplishing a fractionation of the polyampholyte as evidenced by increased inherent viscosity of 20% and more when dialysed for 96 hr. in an aqueous system. The most striking result was in the polyampholyte in which z is 4; here the inherent viscosity increased from 0.19 (c = 0.455 g./100 ml. formic acid at 30°C.) to 0.34 (c = 0.436 g./100 ml. formic acid at 30°C.).The use of membranes such as methoxymethylnylon for the fractionation of polystyrene in non-aqueous systems has been described.3 But despite the very common reliance on dialysis for fractionating natural products such as protein^,^.' enzymes,6 polysaccharides,8 and ligninsulfonates,' we are not aware of its use for fractionating high polymers in aqueous systems. Work on proteins has shown that the arbitrary division between proteins (molecular weight > 10,000) and natural polypeptides (molecular weight < 10,000) corresponds to the division between nondialysability and dialysability through cellophane.* In accordance with that work, we suggest that the higher viscosity of the polyampholytes after dialysis results from the diffusion into the solvent of the smaller molecules present in the polymer mixture.In order to investigate the scope of applicability of this technique, several polymers and copolymers were studied. We prepared a copolymer consisting of 60 parts of methyl methacrylate and 40 parts of acrylic acid. This copolymer would be expected to be somewhat hydrophilic. The inherent viscosity of this material increased Over 10% during 48 hr. of dialysis against distilled water, from 2.99 ( c = 0.462 g./lOO ml. formic acid at 30°C.) to 3.31 (c = 0.443 g./100 ml. formic acid at 30°C.). Nine per cent of the material dialysed out of the cellulose tubing into the solvent. When the nondialysed copolymer was reprecipitated from acetone with petroleum ether (3CrsO0C.), the inherent viscosity increased only very slightly, from 2.99 to 3.03 (c = 0.581 g./100 ml.formic acid a t 30°C.).Two hydrophobic polymers, polyacrylonitrile (winh = 1.65; c = 0.439 g./100 ml. formic acid at 3OOC.) and poly(methy1 methacrylate) (Vinh = 1.05; c = 0.241 g./100 ml. formic acid a t 30°C.) showed no signilicant change in viscosity after 48 hr. of dialysis. The latter polymer did, however, show an improved agreement between theoretica...

A series of three true polyampholytes with unequivocally alternating acidic and basic groups attached directly to the skeletal backbone of the polymer chain have been prepared. This was accomplished by copolymerizing 3,6‐diallyl‐2‐piperidone with the α,ω‐dithiols containing 2‐, 4‐, and 6‐methylene groups. The polymerization was carried out in an emulsion system initiated by 2,2′‐azobisisobutyronitrile (AIBN), yielding soluble piperidone‐containing polymers with molecular weights in the 20,000–30,000 range. The piperidone rings in the polymers were hydrolyzed by dilute sulfuric acid to yield the desired polyampholytes. Fibers were prepared by wet‐spinning formic acid solutions of the polyampholyte into saturated salt solution or by melt‐spinning. These fibers were quite elastic. We were unsuccessful in demonstrating that mechanical energy could be attained by the effect of pH on the fibers. Similarly, no pH effect could be elicited in Instron tests. The stress‐relaxation curve showed a marked positive force–temperature effect characteristic of rubberlike materials with few crosslinks. In a check of transition temperatures, it was noted that on repeated runs the second‐order transition temperature rose markedly, suggesting an irreversible change. Viscometric studies clearly demonstrated polyelectrolyte behavior. X‐ray diffraction studies of the polyampholytes showed that maximum crystallinity and orientation occurred in the polymer containing as part of the repeating unit the 1,4‐butane dithiol moiety.