What causes vegetable fiber to be firmer?

Vegetable fiber becomes firmer due to several factors, including the presence of lignin, cellulose, and hemicellulose in plant cell walls. Lignin provides structural support and rigidity, while cellulose forms strong fibers that contribute to the overall firmness. Additionally, the maturity of the plant and growing conditions, such as water availability and soil type, can influence the firmness of vegetable fiber. As vegetables mature, their fiber content typically increases, resulting in a firmer texture.