Fruits and fruit juices high in acid lemon juice (pH: 2.00–2.60) limes (pH: 2.00–2.80) blue plums (pH: 2.80–3.40) grapes (pH: 2.90–3.82) pomegranates (pH: 2.93–3.20) grapefruits (pH: 3.00–3.75) blueberries (pH: 3.12–3.33) pineapples (pH: 3.20–4.00)