When skim milk at pH 6·55 was heated (75 to 100 °C for up to 60 min), the casein micelle size, as monitored by photon correlation spectroscopy, was found to increase during the initial stages of heating and tended to plateau on prolonged heating. At any particular temperature, the casein micelle size increased with longer holding times, and, at any particular holding time, the casein micelle size increased with increasing temperature. The maximum increase in casein micelle size was about 30–35 nm. The changes in casein micelle size were poorly correlated with the level of whey protein denaturation. However, the changes in casein micelle size were highly correlated with the levels of denatured whey proteins that were associated with the casein micelles. The rate of association of the denatured whey proteins with the casein micelles was considerably slower than the rate of denaturation of the whey proteins. Removal of the whey proteins from the skim milk resulted in only small changes in casein micelle size during heating. Re-addition of β-lactoglobulin to the whey-protein-depleted milk caused the casein micelle size to increase markedly on heat treatment. The changes in casein micelle size induced by the heat treatment of skim milk may be a consequence of the whey proteins associating with the casein micelles. However, these associated whey proteins would need to occlude a large amount of serum to account for the particle size changes. Separate experiments showed that the viscosity changes of heated milk and the estimated volume fraction changes were consistent with the particle size changes observed. Further studies are needed to determine whether the changes in size are due to the specific association of whey proteins with the micelles or whether a low level of aggregation of the casein micelles accompanies this association behaviour. Preliminary studies indicated lower levels of denatured whey proteins associated with the casein micelles and smaller changes in casein micelle size occurred as the pH of the milk was increased from pH 6·5 to pH 6·7.

Skim milk was adjusted to pH values between 6.5 and 6.7 and heated (80, 90, and 100 degrees C) for up to 60 min. Changes in casein micelle size, level of whey protein denaturation, and level of whey protein association with the micelles were monitored for each milk sample. Changes in casein micelle size were markedly affected by the pH at heating. At low pH (6.5-6.55), the casein micelle size increased markedly during the early stages of heating, and the size plateaued on prolonged heating. The maximum increase in size was approximately 30-35 nm. In contrast, at high pH (6.7), much smaller changes in size were observed on heating and the maximum increase in size was only approximately 10 nm. An intermediate behavior was observed at pH values between these two extremes. The rate of denaturation of the major whey proteins, alpha-lactalbumin and beta-lactoglobulin, was essentially unaffected by the pH at heating for the small pH changes involved in this study, and the changes in casein micelle size were poorly related to the level of whey protein denaturation. In contrast, the level of denatured whey proteins associating with the micelles was markedly dependent on the pH at heating, with high levels of association at pH 6.5-6.55 and low levels of association at pH 6.7. Changes in casein micelle size were related to the levels of denatured whey proteins that were associated with the casein micelles, although there was a small deviation from linearity at low levels of association (<15%). Further studies on reconstituted and fresh milk samples at smaller pH steps confirmed that the association of whey proteins with the casein micelles was markedly affected by the pH at heating. These results indicate that the changes in casein micelle size induced by the heat treatment of skim milk were a consequence of the whey proteins associating with the casein micelles and that the level of association was markedly influenced by small pH changes of the milk. It was not possible to determine whether the association itself influenced the casein micelle size or whether parallel reactions involving micellar aggregation caused the increase in micelle size as whey protein association progressed.

No abstract

Gastric schwannoma (GS) is a rare neoplasm of the stomach. It accounts for 0.2% of all gastric tumors and is mostly benign, slow-growing, and asymptomatic. Due to its rarity, GS is not widely recognized by clinicians, and the precise differential diagnosis between GS and other gastric submucosal tumors remains difficult preoperatively. The present study reports a case of GS misdiagnosed as gastrointestinal stromal tumor and reviews the clinical, imaging, and pathological features, treatment, and follow-up of 221 patients with GS previously reported in the English literature. Although GS is rare, the case reported in the current study highlights the importance of including GS in differential diagnoses of gastric submucosal tumors. Furthermore, the findings of the review suggest that although many cases are asymptomatic, the most common symptoms are abdominal pain or discomfort, not gastrointestinal bleeding, and malignant GSs present with clinical symptoms more commonly. Although large-sample multicenter studies on the efficacy, safety, and oncological outcomes of minimally invasive techniques are required, the findings presented herein may be helpful for clinicians when diagnosing or treating GS.