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Apo and holo forms of lactoferrin (LF) from caprine and bovine species have been characterized and compared with regard to the structural stability determined by thermal denaturation temperature values (T (m)), at pH 2.0-8.0. The bovine lactoferrin (bLF) showed highest thermal stability with a T (m) of 90 ± 1°C at pH 7.0 whereas caprine lactoferrin (cLF) showed a lower T (m) value 68 ± 1°C. The holo form was much more stable than the apo form for the bLF as compared to cLF. When pH was gradually reduced to 3.0, the T (m) values of both holo bLF and holo cLF were reduced showing T (m) values of 49 ± 1 and 40 ± 1°C, respectively. Both apo and holo forms of cLF and bLF were found to be most stable at pH 7.0. A significant loss in the iron content of both holo and apo forms of the cLF and bLF was observed when pH was decreased from 7.0 to 2.0. At the same time a gradual unfolding of the apo and holo forms of both cLF and bLF was shown by maximum exposure of hydrophobic regions at pH 3.0. This was supported with a loss in α-helix structure together with an increase in the content of unordered (aperiodic) structure, while β structure seemed unchanged at all pH values. Since LF is used today as fortifier in many products, like infant formulas and exerts many biological functions in human, the structural changes, iron binding and release affected by pH and thermal denaturation temperature are important factors to be clarified for more than the bovine species.

This study aims at providing a comparative evaluation of tomato processing by‐products, i.e., seeds and peel. A pilot scale process has been demonstrated for extraction and drying (both freeze and cabinet drying) of tomato seeds and peel. Various aspects of dried tomato seeds such as its protein content, amino acid profile, calculated protein efficiency ratio (PER), presence of antinutritional factors, polyphenol contents and antioxidant activities were evaluated. In this study, the total polyphenol content in the hydrophilic extract as well as antioxidant activities of tomato peel were found to be 66.5 and 38.2% higher, respectively, than that of the tomato seed meal showing importance of the former from a functional point of view. Tomato seed protein isolate (92%) prepared from tomato seed meal had a calculated PER of 2.66. The protein isolate contained all essential amino acids (including lysine), meeting the minimum requirements of reference protein for preschool children aged 1–2 years (WHO/FAO/UNU). The tomato seed protein isolate showed negligible levels of phytate (3.48 μg/g) and trypsin inhibitory activity (2.655 TIU/mg). This study clearly highlights that tomato seed, a by‐product of tomato processing industry, is a rich source of high‐quality plant protein together with intrinsic polyphenols and antioxidant activities, although the functional properties being less dominant than the peel counterpart. Therefore, tomato seed meal with unique protein quality could be regarded as a potential source of protein‐rich adjunct in various food formulations. Practical Applications With the increased industrial demand of protein sources, there has been an upsurge of research efforts in recent years to extract dietary proteins from plant‐based sources. By‐products of oilseeds, fruits and vegetable‐processing industries can be sustainable low‐cost protein alternatives, which are available at no additional cost and can find commercial valorization in food formulations. As an example, this study identified a pilot plant setup to produce tomato seed protein isolate and investigated protein quality, antinutritional factors as well as compared the polyphenol content and antioxidant activities in the context of its counterpart by‐product tomato peel. This knowledge will facilitate the use of tomato seed protein isolate as a low‐cost protein‐rich adjunct with functional benefits in food formulation. Most importantly, this study highlights that high‐quality plant protein isolates can be recovered from agro‐industrial by‐products, thus adding commercial value to them and allowing their industrial exploitation.

Papain, a powerful proteolytic enzyme, is an endoprotease belonging to cysteine endopeptidase family. It is used extensively in food processing especially in tenderization of meat. In this study, we have made an attempt to show the structure activity relationship of this enzyme and the role of calcium and magnesium ions in the activity and stability of the enzyme. Results of activation and stabilization of the enzyme by these cations showed concentration dependent effect. The enzymatic activity of papain increases to a maximum of 18% and 24% in presence of calcium and magnesium ions at 1 x 10(-3) M concentration, respectively. Thermal denaturation studies showed that the binding of calcium and magnesium ions bring about change in the thermal stability of papain at various concentrations of these metal ions. Far ultraviolet circular dichroic studies showed no significant change in the alpha-helix and beta-sheet structure of the papain upon binding of these metal ions. The mechanism underlying the structure activity relationship of papain in presence of these metal ions have been discussed here with reference to the ionic radii, ligand binding preference, coordination numbers and the electrostatic forces between the protein molecule and cations present in the microenvironment of the enzyme.