Characterization of Biocalcium Microparticles from Saltwater Crocodile (Crocodylus porosus) Bone and Their Potential for Enhancing Fish Bologna Quality

Abstract

Saltwater crocodile (SC; Crocodylus porosus) bone, an underutilized by-product, can be converted into high-value bio-calcium (Biocal), serving as a potential source of calcium and minerals. This study aimed to produce SC bone Biocal as functional gel enhancer for fish bologna development and to increase calcium intake. The resulting bone powder was evaluated for physicochemical, microbiological, and molecular properties. Additionally, the textural, physicochemical, structural, and sensorial properties of the formulated fish bologna incorporating Biocal at varying levels (0-10% w/w) were also evaluated. Biocal, obtained as a fine white powder, had a 16.83% yield. Mineral analysis showed 26.25% calcium and 13.72% phosphorus, with no harmful metals or pathogens detected. X-ray diffraction confirmed hydroxyapatite with 69.92% crystallinity, while calcium bioavailability was measured at 22.30%. Amino acid analysis indicated high levels of glycine, proline, and hydroxyproline, essential for collagen support. The findings confirmed that SC bone Biocal is beneficial and safe for food fortification. Incorporating SC Biocal (2-10% w/w) significantly affected the fish bologna characteristics (p < 0.05). As the Biocal level increased, the gel strength, hardness, and shear force also increased. The addition of 6% (w/w) Biocal significantly improved the textural property, without a detrimental effect on the sensory attributes of the bologna gel (p < 0.05). SDS-PAGE analysis showed TGase-enhanced myosin heavy chain (MHC) cross-linking, particularly in combination with Biocal. Moreover, the enriched Biocal-bologna gel exhibited a finer and denser microstructure. Thus, SC Biocal, particularly at 6% (w/w), can serve as a functional gel enhancer in surimi-based products, without compromising organoleptic quality.

Keywords: biocalcium; fish bologna; functional gel enhancer; saltwater crocodile bone.

Figure 1

Visual appearance (a), SEM microstructure with magnification 2000× (b), and 20,000× (c), as well as XRD patterns (d) of Biocal from SC bone.

Figure 2

Breaking force (a), deformation (b), and gel strength (c) of bologna made from salmon cuts/surimi mixed gel containing 0.05% MTGase and fortified with SC Biocal at varying levels (0–10%). Different lowercase letters denote significant differences (p < 0.05). Values represent mean ± SD (n = 3). Con 1: control bologna gel without MTGase and Biocal; Con 2: control bologna gel containing MTGase without Biocal added; Biocal 2, Biocal 4, Biocal 6, Biocal 8, and Biocal 10: Biocal-fortified bologna gel at 2, 4, 6, 8, and 10% (w/w), respectively, and incorporated with MTGase.

Figure 3

Visual appearances of bologna gel (a) and slice (b) from salmon cuts/surimi added with SC Biocal at different levels (0–10%). Con 1: control bologna gel without MTGase and Biocal; con 2: control bologna gel containing 0.05% MTGase without Biocal added; Biocal 2, Biocal 4, Biocal 6, Biocal 8, and Biocal 10: Biocal-fortified bologna gel at 2, 4, 6, 8, and 10% (w/w), respectively, and incorporated with MTGase.

Figure 4

Protein pattern of bologna made from salmon cuts/surimi mixed gel containing 0.05% MTGase and fortified with SC Biocal at different levels (0–10% w/w). HMP: high molecular weight protein; MHC: myosin heavy chain; AC: actin; TM: tropomyosin M: standard protein marker; C₁P: control bologna paste without MTGase and Biocal; C₂P: control bologna paste containing MTGase. Numbers designate the amounts of Biocal added (%).

Figure 5

Scanning electron microscopic image of control and selected bologna from salmon cuts/surimi mixed gel containing with 0.05% MTGase and fortified with SC Biocal at levels of 6 and 8%. Magnification: 13,000×.