Conformational Changes in Serum Pectins during Industrial Tomato Paste Production

Abstract

It is well-known that an irreversible decrease in serum viscosity occurs when tomato juice is concentrated by evaporation into paste. Several studies have suggested that the loss in serum viscosity is due to pectin depolymerization, caused by the high temperatures used during industrial tomato paste production. This study demonstrates that conformational changes in pectin may play a more important role than pectin depolymerization in the irreversible loss of serum viscosity during industrial tomato paste production. Samples of tomato juice, processing intermediates, and paste were obtained from a commercial producer in California. After dilution to 5 degrees Brix, tomato serum was obtained by centrifugation at 15000 g for 10 min. Weight average molecular weight (M(w)) and root-mean-square (rms) radius of the polymers in the tomato serum were determined using high-performance size-exclusion chromatography with multi-angle laser light scattering and refractive index detectors (HPSEC-MALLS-RI). Serum viscosity decreased throughout the juice concentration process, especially at later stages, where the processing temperature reached a maximum of 90-95 degrees C. In parallel with this decrease in serum viscosity, there was an increase in the soluble pectin concentration. Analysis of the M(w) distribution of the tomato serum showed that solubilization of pectin occurred across the entire polymer distribution range. The M(w) changed from 2.62 x 10(5) g/mol in the juice to 2.61 x 10(5) g/mol in the paste, indicating that minimal depolymerization occurred. However, the rms radius distribution indicated that the pectin conformation became more compact as the juice became more concentrated. Conformational plots revealed that serum pectins in the hot-break tomato juice and at the early stages of concentration behaved as extended coils, having shape factors of about 0.40. In processing intermediates taken from later stages in the process and in the paste, the shape factor changed to about 0.25, indicating a more compact conformation. This conformational change correlated with the observed decrease in serum viscosity in the paste production process. This result is consistent with a Flory-Fox-type relationship between viscosity, rms radius, and M(w). The conformational change may be due to increased polymer-polymer interaction brought about by the concentration process.

A Review on the Relationships between Processing, Food Structure, and Rheological Properties of Plant‐Tissue‐Based Food Suspensions

“…The low pH value of tomato‐derived products may hamper the β‐eliminative pectin solubilization and degradation (Keijbets and Pilnik ; Kravtchenko and others ; Krall and McFeeters ). Furthermore, chemical pectin demethoxylation and conformational changes can occur during thermal processing at high temperatures (De Roeck and others ; Diaz and others ).…”

“…So far, the literature describes a broad variety of procedures to examine the serum characteristics, in particular pectin composition. Whereas the pectin concentration is often determined by colorimetric measurements of the GalA content, the pectin molar mass is generally analyzed by high‐performance size‐exclusion chromatography equipped with a multiangle laser light scatter detector (Diaz and others ; Moelants and others ). The DM can be calculated as the ratio of the molar amount of methoxyl esters to the molar amount of GalA and can be measured colorimetrically, through infrared spectroscopy, and other methods (Lima and others ; Moelants and others ).…”

The effects of bruising and temperature on enzyme activity and textural qualities of tomato juice

“…The trend in serum viscosity correlates well with the production of methanol ( R 2 = 0.98; data not shown), which reinforces the hypothesis that enzymatic depolymerization and solubilization of pectin molecules is causing a decrease in the consistency at the higher temperatures used in this study. However, loss of serum viscosity at the higher temperatures may also be due in part to conformational changes in the pectin molecules caused by thermal treatments rather than enzymatic depolymerization …”

“…However, loss of serum viscosity at the higher temperatures may also be due in part to conformational changes in the pectin molecules caused by thermal treatments rather than enzymatic depolymerization. 28 Per cent total solids, soluble solids and insoluble solids were not significantly affected by pre-treatment temperature (P >0.05) (data not shown). Other studies have shown that Bostwick value is directly correlated with solids content.…”

Effect of Processing Methods on the Quality of Tomato Products

“…One type of commercially available pectin forms a gel after thermal treatment at 95˚C (203˚F), followed by cooling [10]. The high temperature facilitates a dissociated, disordered pectin conformation that facilitates the extraction process [11]. Similarly, hemicelluloses respond to high temperature in the same manner [12].…”